The animation system is not much more advanced than just being a series of images in a row that gets played. Timing multiple animations for a loop can be a bit tricky but there might be certain animations you can just delay off screen for a few frames or something to make it fit.
I’m not sure what you mean with tagging and copying out really but there is a tag system (press F2 after selecting a range of frames) but this is really just for looping a section to see for yourself or for exporting specific sections.
I would just recommend selecting all your cels and selecting Frame -> Duplicate cels which will just double the animation after the last frame.