In my job they're already using a modified Bootstrap template and it's working fine for everything in Symfony2 but I would like the CRUD's generated by Symfony2 to have Bootstrap 3 structure so it gets styled by it.
Currently I've found:
I used to have to perform my own form modifications as well. However, Symfony 2.6 introduces support for Bootstrap 3.0 for forms:
So if you upgrade to Symfony 2.6 you should have that built in.