Completely restart Bash

Have it replace itself with itself.

exec bash -l

Note that this won't affect things such as the cwd or exported variables.

I urgently suggest to log in on a separate window/screen. This way you still have a working session if something goes wrong with your changes to startup files. Also you are sure to have a clean environment.

Reason: I saw too many people locking themselves out of a system because of a simple typo in their .profile (or such).

If your goal is simply to read the modified files again, you don't have to restart it. You can simply source it.

source filename

or

. filename # notice the dot

Note that this won't give you a "clean state" in a sense that it won't unset any set variables or defined functions...