First thought: Email Warmoth customer service and see if they can do a 24-fret-pickguard reposition as an off-menu option.
Plan B: If the Bridge pickup is going to be the same type as the neck pickup, and if you have a router: Make a pickup template from a piece of 1/2” MDF. Attach the pickguard to the MDF with double-sided tape. Drill or plunge route a starter hole in the MDF. Then use a bearing bit to carve the MDF out in the shape of the pickguard slot. Gotta be careful as the pickguard itself isn’t very thick, so you’ve got to very carefully set the depth of the bearing. This would be easier to do on a router table than with a handheld router.
Option 3: Hand tools. Put some masking tape or painters tape on top of the pickguard, then grab a pencil and a ruler and draw the cutout. Make a starter hole, then use a coping saw to cut out the hole. Be conservative with the saw, stay a bit inside your pencil lines. Then use files and/or sandpaper to clean up the cut and get it to final size. Test fit the pickup as you go so you don’t take off too much material.
Alternatively you could follow the Option 3 steps to make an MDF template. If you screw up, you only waste the MDF, not the pickguard. Then use the router to make the hole.