Mixed RA4 developer is almost eternal in terms of shelf life! It can also develop an enormous number of prints. I have never counted.

In normal RA-4 process, it discolors (usually to dark magenta) because of the dyes released from papers. This doesn't mean it would be dead! You can use the developer as long as you get good blacks with your usual developing time, the dyes from papers that make it dark do not affect the process in any way.

Naturally, in the reversal process, these dyes end up in first developer, stop and wash water, so you can maintain the original color of the color developer. In the terms of number of prints, it is no different from normal RA-4. And, you can use the very same developer between these processes, just make sure you wash the papers well before going to color developer.

If you decide to make a "low contrast color developer" by adding sodium/potassium sulfite at about 0.5 g/l, you can also use it for both processes for the same lower-contrast effect.