It depends = What charter company did you choose & what anchorages do you plan to visit in SXM?
In '05, I chartered from Sunsail (french side) and never took the yacht to the dutch side - I visited Grand Case, Marigot & a couple more french anchorages on NE coast.
With regard to Anguilla, It was easy - 15 mins (in) but longer out due to carnival 20+mins. Coming back to SXM (Marigot) I do not remember (i do not have access to my notes at the moment) doing anything or if we did it was very easy.
I visited the Dutch side (Simpson Bay) of SXM via dinghy from Marigot = go under nearby bridge in Marigot & make your way = piece of cake
BTW - I think Horizon Charters is in Simpson Bay (dutch side)
Don't worry, the charter company will have all the local knowledge & hints. Dress appropriately, be respectful, follow the rules, use the right forms and it will be painless.....no matter what island / country.