No way... UFT will not reinstall the templates as long as you do not touch the GEDCOM tags. I translated all the events and when importing data all went well my translated templates were still there!
One 'role' you have to be carefull with, in the event 'occupation' the first role is 'employee' and you cannot touch him because otherwise with import from gedcom UFT does not find the 'employee' role and it will create a new role.
This means that UFT is so good that it will not change or overwrite altered templates but rather create new events and roles in addition to the existing ones. The created events and roles (and sources) are taken from the reference templates.