Here's the picture

We have an application for a vertical market.

Situation that we will be confronted to enventually:

Customer asks for modifications that will apply only fot their business.

Do we tell them that we don't do those or do we do it?

What would be the best way to manage future developments after that customization.

Because after that we'd be stuck with our glocal application but also one (and possibly more if we agree to do those customizations) variations based on our global application.

What would be the best way to manage a possible mess?