I usually do it this way..
(lets say I want a 1 bar count-in before the start of the new tempo)..
I create a MIDI track, routed to a metronome sound, and record one bar of click during the first bar of the new tempo.
I then switch that MIDI track over to Linear Timebase, set Snap to "Events", then drag-copy that one bar click Part backwards, such that the end of the copied Part butts against the start of the original. (If necessary I can then delete the original, although I am more likely to want to keep it).
Thanks, as always, vic_france.
(Is there a one-click macro to type out that above phrase?? :D )