This post will ramble a bit so be patient with me...
Not every component supports discrete codes for each and every function. In general, the known codes, along with basic JP1 info is at
[Link: hifi-remote.com] So no, your Yamaha may not have just a toggle power function (note, I'm not saying it doesn't have one. I haven't had time to check.) I use a baby Yamaha in my 2nd setup and it uses discrete power on/off and I just went with it. (Truthfully, most users want the discretes, not the toggle. And to my knowledge, in general, Yamaha receiver codes are universal. Note not all of the functions are supported by every model. So if yours doesn't support a 70mm Sci-Fi mode, you can't use that code.)
That said, because JP1 allows users to be very creative with their OFA remotes, there may be lucky occasions where new functions are discovered (IOW, things that will function that the manufacturer never told us about.) In my own case, I recently discovered that my Denon receiver allows me to jump to certain volume settings. And I obtained those codes with some help from the JP1 gurus over at the OFA forum here at remotecentral.com. And yes, if you're lucky enough to get the codes into your JP1 remote, then you just teach them to your 500.
You mention downloading of files. I haven't been over to the JP1 Yahoo group for a very long time. Do you mean that there are device files over there for your equipment? If so, this route could work for you. But here at rc.com, the file download area doesn't have JP1 device files. For the MX-500, the files that are usable are the IRClone .m5 ones (of course) and with the help of Mr Solley's CCF to .m5 convertor, Pronto .ccf files. BTW, you asked if you can grab and use Pronto files for your 500. Yes, but only by using the IRClone and Mr Solley's convertor. As for the 500e software, it is a free download at IRClone. You need the IRClone box to make it work and an IRClone purchase code key to allow you to save files. But the software is available for download for nothing @
http://www.irclone.comNext to last answer...I agree that JP1 is kinda tough to get a handle on. I only use it when I have to because I just don't get it. I had to be coached thru obtaining the Denon codes I recently wanted. I couldn't have done it alone. Still, I'm very grateful to the JP1 group and it's creators. IMO, they're geniuses!
Finally, my best advice is to start a thread and ask for help on the particular devices that you're struggling with. Do this before you buy anything extra. I would help more but this week is not good for me time wise.
I hope all the clutter in this answer helps...