The game effects were as follows:
If you stop firing your weapon, a field of some sort develops around the valkyrie. If you touch certain enemies with this field, they convert to your side and start shooting at enemies. You can only do this with one enemy at a time, and once I had one I was never able to get a different one (it stayed with you), so I always did my best to wait for a Glaug or Nas-Jer to show up and use it on them
I could swap out pretty good.
You just gotta make sure the guy you're tagging is stealable. Otherwise your old guy retreats and you don't get a new one.
Also, since the Minmay Beam is the same size and shape regardless of mode, Fighter mode is best for vertical tagging, and battroid mode is best for horizontal tagging. Otherwise you get a lot of ramming damage(F mode is especially bad, as horizontal tagging is easier than vertical and the nose of the Valk touches the front edge of the Minmay Beam).