1. Can I use PPG Concept over the Imron?

I'd stick with the paint that's on there (Imron)

2. How do I blend the spray edges into the Imron for a seamless finish?

Hi Brian,
Blending paint is a difficult proposition at best. The first issue is
color match, Imron shouldn't fade, but get the original color if you
can find it (should be in the log book). Then try a little spot (dab
from your pinkie) to see how it looks, remember it will dry a tad
darker than the wet color. The area where the paint is to go must be
lightly sanded, go beyond the intended paint area a good 6 inches in
all directions with 220 dry sanding. Then mask at the edge of your
extended sanding. The trick is to never touch the masking tape with
sprayed paint or you will build up a lip and when trying to wet-sand-
out this lip, you will sand too deep on the original paint and start
to show the underlying primer. Ugh, I hate it when that happens! Only
thing to do then is to expand your paint area another 6", re-mask and
paint again. If you do it right the first time, the over-spray will
fall well short of the masked area and is easily wet-sanded out with
600 wet, followed by 800 wet, then buff after 3 days of paint curing
time.
Good luck, it only took me 30 years to figure out the above and don't
ask me to do it voluntarily.

Aircraft are designed by geniuses to be flown by idiots!
JJ