Galactus

I have a very good player at QPR called simon walton but hes only a natural dmc which i currently dont include in my system

hes also accomplished in cb and cm

so if i retrain him in any of these positions will he ever exceed 18 stat points for either of them?

SWaRFeGa

I don't think you can turn "Accomplished" into "Natural"

Scotty Walds

Maximum is 18 when training a new position, or improving an 'Accomplished' one already set

Hawshiels

Scotty has answered the question you asked, but if you are now thinking of training him in a position other than one in the centre, (i.e. a position on the left or right), bear in mind that he will lose the 'free' attributes that come with these central positions and it will take up 'current ability' points that may be valuable if used elsewhere in his profile. If you're not familiar with this, either read this, or forget I spoke if it's not relevant to you.