Kind of like how Triangulate automatically turns on when you switch to BTN/MIN. Since you can still make NQ/HQ items even with Collectible Synthesis on, there is no harm done with this. Some of these recipes require mats from 3-4 different crafts so I'm constantly changing classes and it's a hassle having to turn it on every single time.
I wonder how many "HQ" items others have made by mistake xD When aiming to make collectables....
I've done this so many times now.... xD maybe just me!
As it activates as a skill, can't you just add it to your switch macro?
/macroicon 1 gearset (change to the gearset for that craft, so, if Weaver is number 5 on your gear set list, change it to /macroicon 5 gearset)
/gearset change 1 <wait.1> (as above, the required gear set number)
/ac "Collectable Synthesis" <me>
Just checked, works perfectly fine (don't forget that <wait.1>