Only the main file (the one that you would open in Pd) must be called main.pd then the other .pd files should just live in the same folder. If you get a "couldn't create" error, it means that the abstraction could not be found.
Have you updated your board recently? I seem to remember an older version of the Bela IDE would replace "~" in filenames with "" but this should be fixed now. So if you get the "couldn't create" error, see if your rev~.pd files show up in the IDE with a "~" or a "_".
On a side note, if you were to exceed the CPU usage, you would get a "blocks dropped " message instead, or the IDE would just hang and display the "you have been disconnected" message. If the latter happens, you will need to press the button on the Bela cape to forcibly stop the running program and re-gain control of the IDE