Is it too late?

[Big_Daddy]

I just primed my A-10 and noticed a few seams I need to fix. Can you fix them after priming???

[Leigh]

Absolutely, that's one of the main reasons for priming so you notice the flaws you missed. I'll usually prime, clean it up, wet sand with 600 grit, prime again clean it up a bit again if needed, wet sand with 1000 grit or smaller, prime again. Some models can get four or five coats of primer but these are thin mist coats and often the sanding takes the bulk of the primer off.
As for your seams there are as many methods of taking care of them as modellers, one I only learnt recently 'cos people often forget to mention the basics, if its a fuselage type seam with a ridge just scrape your exacto knife gently along the seam at right angles to it. saves alot of sanding.
If its a seam that needs filling I prefer auto spot and glazing putty, the red stuff and this method  seams.
Typewriter correction fluid is good for small spots.

In answer to your question no it not too late it's exactly the right time.

[Big_Daddy]

Thanks Leigh!