Decal question

I never cut before applying. I apply the decal and make sure it's properly placed and carefully blot from the center out then I apply Solvaset to melt the decal down into every tiny irregularity. If the recess is too deep then I wait for the decal to be dry and then using a new  #11 blade carefully slice along the line or the area in question then apply Solvaset again. Works for me every time.. 

Make sure you have a good gloss coat on to eliminate the possibilty of silvering under the clear carrier film.

It depends on how fragile the decal is and how deep the recess is where the decal will be split.  If it is a shallow recess like a panel line, you can split it before or after.  If it is deeper like where a flap meets the wing or tail then it may be better to cut first.

If you can scan the decal and print it on regular paper.  Make sure to print at or close to the same size as the actual decal.  Wet the paper so that it is soft but not so wet it falls apart.  Practice with the paper copy and this can help determine which way to go.

Since the wet paper will stick to the model and also conform to the contures you can get a better idea if cutting or not will work.  Just remember that the paper, even wet is not as fragile as a decal so factor that in as you practice.

The paper decal will also indicate where best to cut the decal.  You can print off a few practice decals and try both wet and dry.