Is there some way to program a change over from autonomous mode to RC mode without purchasing the competition switch?
Yes. If you’re using Robot C then to switch you need to download your program to the robot, go to the robot tab → debugger windows → competition control, and select it.
or program your program to run when you hit a certain button on the remote
Do be careful, though - the RobotC competition control debugger window acts similar to regular competition control but not identical to it. We had an issue with our first game at state because our code didn’t play nicely with the competition network even though it worked fine with RobotC’s.
The only two ways to truly mimic the competition network at a match are the VEXnet Competition Switch or an entire VEXnet Field Controller Kit.
For most stuff, RobotC will be fine, but if you go that route, find a team at one of your tournaments with a competition switch and make sure the robot functions properly before putting it on the field.
Check out this thread:
https://vexforum.com/t/competition-switch-wiring-diagram/20401/1
The second post (by jpearman) shows how simple the competition switches are. There really isn’t any electronics. It is literally just a set of switches. If you can read a wiring diagram you could build one of these out of any old switches and scrap wire you have lying around.