there is nothing in the rule book that says you cannot switch cues. .the gray area is what constitutes a playing cue.
to avoid conflicts concerning the gray area if i switch to my break cue to make a jump i finish the inning out shooting with it. nothing in the rule book states you cannot shoot with a break stick.
APA you can not change cues. From the rule book
"Massé and jump shots are legal, when executed properly (see MASSÉ
SHOTS and JUMP SHOTS described in Definitions), but such shots
must be attempted using a regular shooting cue (see REGULAR
SHOOTING CUE described in Definitions). Players are not allowed to
break down their cues or switch to specialty cues (such as cues designed
for jumping and/or breaking) to attempt massé or jump shots."
I do not know about other leagues. Trying to bend the rules, you might be able to get away with it. I have been known to play with my break cue but never in league. If I started a match with it, I would in clear conscious have no problem using it for jumps etc. But I would never try to bend the rule to the point of playing with my player and claiming to just change to a different play cue and use my j/b. I