what i did with my arches after i had the welding done:

mask off the area you dont want paint on,

prime area

rub down fully till completely smooth

prime again to see for any high spots

remove masking tape

rub down till smooth (the lip of the primer where the tape was) and degrease area

very carefully feather the paint in, as long as it is a good colour match it should come up very nicely. I did the arches so they are mega visible and you cant tell!

Good luck mate and let us know how you get on! It was my first time painting such a high profile area and i was more than happy with the results.. I thought to myself it needs respraying but if i can do it on the cheap then im only loosing the cost of a few Halfords aerosols!