SharePoint Online Update: Major Changes to Custom Scripting and Classic Publishing Sites Coming September 2025

If you're managing SharePoint Online environments, there's a significant change on the horizon that you need to prepare for. Microsoft has announced important updates to custom scripting capabilities and Classic Publishing site creation that will take effect on September 15, 2025. Here's everything you need to know about these changes and how to prepare your organization.

What's Changing?

Microsoft is implementing three major changes that will fundamentally alter how custom scripting and Classic Publishing sites work in SharePoint Online.

Important note: If you already have Classic Publishing sites, don't panic. Existing sites remain completely unaffected and can continue normal operations, including creating subsites.

Custom Scripting Gets Disabled by Default

Starting September 15, 2025, custom scripting will be automatically disabled for several SharePoint Online templates. This means the DenyAddAndCustomizePages setting will be set to $true by default for:

This change is driven by security considerations around ungoverned scripting, as Microsoft continues to tighten security controls across its platform.
- BLANKINTERNETCONTAINER#0 (Classic Publishing Portal Site)
- CMSPUBLISHING#0 (Classic Publishing Site)
- BLANKINTERNET#0 (Classic Publishing Site Blank)
- CSPCONTAINER#0 (SharePoint Embedded Site)
No More New Classic Publishing Sites

Perhaps the most significant change is that users will no longer be able to create new Classic Publishing site collections or activate publishing features in existing sites. This restriction applies to both user interface interactions and API calls.
The following templates will no longer be available for new site creation:
- Publishing Portal Site
- Publishing Site
- Publishing Site Blank
- Enterprise Wiki
- Enterprise Search Center
- Site Directory
- News Home Site
- Product Catalog
- Report Center
- Topic Area Template
Improved Property Bag Management

There's some good news in these updates too. Microsoft has introduced a new feature that allows users to manage site property bag values without needing to enable custom scripting. The new setting works at both tenant and site levels, making property bag management much more straightforward.

AllowWebPropertyBagUpdateWhenDenyAddAndCustomizePagesIsEnabled

How This Impacts Your Organization

These changes will have different effects depending on how your organization currently uses SharePoint:

For Custom Scripting Users:

When custom scripting is disabled, several features become unavailable:

Script editor web parts stop working
Custom master pages and page layouts can't be created or modified
Various other customization features are blocked

For SharePoint Administrators:

You'll lose the ability to create new Classic Publishing site collections or enable publishing features at the site collection level through standard methods.

For End Users:

The impact will primarily affect those who rely on custom scripts and Classic Publishing features for their daily work.

What You Need to Do Right Now?

Microsoft recommends taking several proactive steps to prepare for these changes:

Communicate with Your Users
Start informing owners of Classic Publishing sites about these upcoming changes immediately. This gives them time to plan and potentially migrate to Modern SharePoint sites, which Microsoft strongly recommends.
Consider Migration to Modern Sites
Microsoft provides comprehensive guidance for modernizing SharePoint environments. Modern sites offer better performance, security, and user experience compared to Classic Publishing sites. Now is an excellent time to evaluate your current sites and plan migrations where appropriate.
Understand Your Temporary Options
Microsoft has provided several PowerShell commands that offer temporary relief if you need more time:
Delay enforcement for your entire tenant until March 15, 2026:
```
Set-SPOTenant -DelayDenyAddAndCustomizePagesEnforcementOnClassicPublishingSites $true
```
Allow temporary custom scripting for a specific site (24-hour duration):
```
Set-SPOSite <SiteURL> -DenyAddAndCustomizePages $false
```
Allow creation of new Classic Publishing sites (if absolutely necessary):
```
Set-SPOTenant -AllowClassicPublishingSiteCreation $true
```
Update Your Tools
Make sure you're running the latest SharePoint Online Management Shell (version 16.0.26211.12010 or higher) to use these new commands.

The Bigger Picture

These changes are part of Microsoft's broader strategy to modernize SharePoint Online and enhance security. Classic Publishing sites were built for an earlier era of web development, and Modern SharePoint sites offer significant advantages:

Better mobile responsiveness
Improved performance and loading times
Enhanced security features
Better integration with Microsoft 365 services
More intuitive user interfaces

Planning Your Response

Here's a practical approach to handling these changes:

Short-term (Before September 2025):

Audit your current Classic Publishing sites
Identify which sites truly need custom scripting
Plan communications to affected users
Test Modern site alternatives for critical functionality

Medium-term (September 2025 - March 2026):

Use the temporary opt-out period to complete migrations
Train users on Modern SharePoint features
Update any automated processes that create Classic Publishing sites

Long-term (After March 2026):

Complete migration to Modern sites where possible
Maintain only essential Classic Publishing sites with proper governance
Regularly review and optimize your SharePoint environment

Final Thoughts

While these changes might seem disruptive, they represent Microsoft's commitment to providing a more secure and modern collaboration platform. The temporary opt-out options give organizations breathing room to plan and execute transitions thoughtfully.

The key is to start planning now rather than waiting until September. Use this time to evaluate your current SharePoint usage, communicate with stakeholders, and develop a migration strategy that works for your organization.

Remember, existing Classic Publishing sites will continue to work normally, so there's no immediate crisis. However, proactive planning will help ensure a smooth transition and might even lead to discovering better ways to accomplish your current tasks using Modern SharePoint features.