Since I can't seem to find a way to do this, I'll simply shift the responsibility over to the script programmer and return an error instead, asking the programmer to wait for a signal before trying to transmit again.
I don't need to pause the computer but to rather pause the execution of the program (something that event.pull in Lua can do). Returning false or throwing an error is a bit of a breaking API change and differs from the ComputerCraft approach, so I'd prefer to not use it. However, it could be a good idea to send a signal either way to allow catching it, but I'd still need to enforce the limit by waiting a certain amount of time in the callback.
I don't think this is possible and I also don't know why you want to pause the computer for that. I think its better if you enforce the limit by returning false or throw an error. But by pausing the computer it will not be able to handle other events like network or touch events. So this would not make much sense.
The forums are more for coding in game in Lua. At least that the most responsive part of the community in the forum. Many of the maintainers of opencomputers and companion mods hang out in the discord and irc chat regularly. Be patient with them.