Shouldn't be difficult to repot it at all, as you pot on most peppers and chillies as they grow larger each year routinely.
However, as the plant has already set fruit you probably won't gain anything for this year's yield, but it should aid the vegetative growth to give you a larger plant for going into this winter and thereafter for next year.
In future, repot it just as it is getting into growth in the spring.

Thanks Bertiefox - will give it a go. Was afraid I'd send it into 'shock' (as I know it should have been repotted in Spring). It's looking so healthy. I'm new to all this and am finding this site invaluable.....