Haven't tried it (yet), but a Pixel string controlled by the Tiger TP3244 has the option of setting a divider (Pixel Grouping). If you have 36 pixels and set that value to 6, then it behaves as a 6 pixel string. Set it to 9 and it becomes a 4 pixel string. Set it to 36 and should behave as a single string.
But - as of now, I don't think you can change it "during a show" just during initial configuration of the TP3244 or between sequences.
dmoore - you may have hands on experience - do I have that right?
Currently only through initial configuration but its a feature thats being looked into as it really is a firmware thing.