I don't believe xlights supports multiple timing grids currently (or in LOR terms multiple tracks). I am hoping eventually it might. It might be bit advanced for this point in time?
I've been thinking that eventually xlights would greatly benefit from having "multiple timing grids" ... instead of just one ...
and especially the ability to import timings (as is done when defining a new musical sequence currently) but maybe a new option for import a "import timing marks from EXISTING channel(s)" from a pre-existing channel ... so in your example,
if you already had some old programming for a megatree and lets just say it was a red channel ... you
could create a new timing grid based on a channel (or possibly range of all megatree RED channels) and any timing marks
that were used (programmed an ON or FADE UP or FADE DOWN within) for that channel (or range of channels) would be turn into a new set of xlights timing marks based on how they were programmed, unused timings would not be retained