I would like to give a general advise to Xojo Starters and Parttime Devs like myself.
We often read in this Forum that as Projects grow bigger, there's sometime the need to change the behaviour and/or design of a Control used throughout the Project. Which means the Devs need to update all instances of the Control within the Project. Not always this can be done via "Replace all". I've experienced it in my own Projects more then once.
My advice would be to Subclass each new kind of Control used in your Project, even if you do not plan to modify it. And if there's a need at some point to add a Feature to a Control or to change the Design of a Control across the whole Project, you simply do the needed changes to your Subclassed Control. AFAIK: The changes will then automatically be used across all instances of this Control Subclass.
I did not try this, but i think it is possible to make Subclasses of Controls an external Ressource.