Canvas upgrade process

Is it possible for Canvas upgrades to not remove bootstrap themes from existing applications when upgrading.

For example I have a bootstrap theme in the bootstrap css folder. The theme is called ‘Finance’. It sits in the folder C:\CWAS\webapps\finance\assets\css\bootstrap.

Having a new theme in here allows me to select the theme in the admin section. Not sure if this is the preferred way to rebuild the CSS.

When Canvas updates it removes the theme from the folder. It would be great if these custom themes could be left. Maybe some kind of naming convention so they can be identified.