Just got back from a few days (Epcot, MK, HS). Did this exact thing - worked great. I “walked back” a few lightning lanes to line up with ones that were booked for later.
Example: I had a Soarin for 5 pm, but Living with the Land for earlier in the day. I kept randomly modifying to keep pushing the Living back to be closer to 5. Also did this at HS with a few things. Moved one LL back past a lunch we had booked. So glad the modify feature is there now.