Well, it may only happen when the next version of Trisquel is released.
Usually, regular updates are only security and bug-fix ones...
Some trisquel-* are updated from time to time (yesterday for instance!) what
should mean (although I have never tried to check) that the default install
changes.
If you remove some trisquel-* you may only miss these new choices for the
default install (and, again, no "real" software would be removed with it)...
but, once the next Trisquel released, you will be able to remove the PPA and
the Gnash package it brings (the newer Gnash package will be in Trisquel's
repository) and reinstall the trisquel-* packages you want, hence back with
the default choice of softwares (+ the ones you have installed so far).
Am I clear?
