If I understand you correctly, I don't know of any way you can assign a track to be part of a group, but then not be a part of that group while it's still assigned to that group.
What you CAN do is solo just one track out of a group. So for example, suppose you had a group called Strings which has track 1 - violin, track 3 - viola, track 6 - cello, and track 7 - contrabass, and you wanted to hear just track 6 without redoing your assignments or changing the group. The solo override function based on ctrl-clicking a solo button can do this.
1. I'll assume you've created a group as described above.
2. The group works normally - click once to solo or unsolo all the solo buttons in the group.
3. Suppose you want to solo only track 6. Turn off the group, then ctrl-click the solo button in track 6. Now you'll solo only track 6.
4. To return to the group, ctrl-click on the track 6 solo button to turn it off. Now all the grouped buttons are turned off, so you can click on any group button to turn the group back on. Or, ctrl-click on buttons to turn on individual solo buttons within the group.
If in step 4 you don't turn off the track 6 solo button, now if you click any other solo buttons in the group they'll turn on, but 6 will turn off. The grouping is complementary - in other words, clicking on any button in the group will turn off 6 but turn the others on, or turn on 6 but turn the others off. This is handy for when you want to drop something out, then hear it in isolation.
BTW - I removed the previous comment about assigning multiple groups because the way it was worded was misleading - I didn't make it clear you could assign different groups to
different parameters in the same track, but not to the
same parameters in the same track.