I also have an STL-V6 but the size of the ledboard you mentioned was 25mm. So there is lots of room for a 20mm (or 16mm) ledboard with your emitter of choice.
Of course there are BLF members who don’t have a screwdriver, who rely on others to execute their mods. But this one is really easy. So you can either reflow an emitter, or you can try to find a copper or brass ring that fills the gap between 25mm and 20mm (or 16mm). Unless.
Find yourself a round piece of plastic (ring) that fits the opening of your reflector. If it fits, you cut off a piece of about 3mm length. Make an opening in the middle of the piece of plastic of a size that fits the four corners of the led. Superglue that ring on your new (20mm?) leadboard. Now you have something that aligns the reflector and the led. It takes charge of the centering, so to speak.
For focussing (and preventing shorts) I use a piece of (nylon?) sheet with a hole that fits the glued-on plastic ring. I myself am fond of the type of sheet you find in “a box of chocolate”. Add as much selfmade shims to find the correct focussing.
If this all sounds jibberish, read the LINK
PS That Fandyfire is a superior host! But who am I to judge……