I was interested in your problem. Did you manage to resolve it?
In my experience there is no easy answer. The only way is to painstakingly clean any excess of at the time (a bit like bricklaying) and smooth the line out - small bits can be removed later but it is tedious. If do you leave it till later its very difficult to remove.
I have a problem with old white tile grouting that has turned black in places. Do you know of any way the black can be cleaned off without digging it out and re-doing it. Alternatively is there anything it can be cleaned with which will stop it turning black in the first place.