Without affecting the alignment of midi notes recorded to video frames, what settings control this? In other words I wrote out midi parts to sync with video spots and then decided to increase tempo at a certain spot and then bring the tempo back down, everything to the right of the tempo change now is out of sync with the video. 
Generally you need to Insert time, however this will affect the video (or audio) which may not be a problem if there are scenes involved.
You can insert a time signature change such that there are more beats to a bar or more measures, which will allow you to insert additional tempo changes that may be quicker in terms of time but it can be quite involved when determining whether to use jumps or ramps.
Not sure I´m understanding you correctly, but MIDI parts that should stay on a fixed video frame must reside on linear timebased tracks, and MIDI parts that shall follow the tempo changes and stay on a certain bar must reside on musical timebased tracks.