I have found these two references on boot-loop problems disabling the stagefright booleans in build.prop:
The user in the final post did not preserve ownership/permissions on the build.prop file. His boot-loop had nothing directly to do with disabling stagefright.
I used the busybox vi editor with an external keyboard to change my build.prop, obviating this issue.
I have seen no clear evidence that disabling stagefright will harm the Android OS if done correctly and with care (YMMV).