Cat rigs allow you to do this mostly on the fly while sailing (with exception of diamonds)
A common A cat mast adjustment is diamond tension that can be adjusted while sailing. This is done by terminating the diamonds at a lever and then running a set of pulleys to a block which can be controled while sailing. See picture.
The nice thing about this setup is you can start with diamonds fixed to the bottom of the mast and shorten them later to the adjustable system.
Bill
