Based on experience, when you send the watch to Swatch Service Centre, they will have a look at the watch and tell you if they can do it, locally. If they cannot do it, they will ask you if you want to send it back to Bienne. They do have a fixed price for the service and shipping is included in the quote. You will have to decide if it is worth it to send the watch. You can tell them what parts you want them to replace and what parts you do not want them to replace, but this have an impact on the service warranty. Be prepared to wait as it can take time to get the watch serviced. The last time my brother sent his Omega from the 40s it took Bienne 6 months to turn the watch around.
Other option is to go international. End of the day it comes down to the value of the watch and what it means to you.
As for RSC, I have not had much problems with them. They usually quote (my experience anyway, both in Malaysia and elsewhere) upfront what requires to be changed and the estimate cost of replacement. Along the way, if there are other parts that needs to be changed, they will call you to inform you of the cost. This is where the practice differs from RSC to RSC. Some RSC have what is called a fixed package pricing. They will quote upfront the cost of repair and a fixed service package. For parts that they have to change along the way, falls under this fixed package. Usually this price is about the cost of replacing the movement as the replacement cost for the other parts is already quoted, e.g. stem tube, winding stem, gaskets etc and the only 'surprise' left is the movement. This service package price is not very much, safe to say that it is about RMxxx (below a grand). Also you can tell them what you want to replace and what not to do with the watch, e.g. do not replace the dial of your red submariner or polish your vintage submariner reference 5512.
The RSC will also tell you if they can provide you with a service warranty, full or otherwise. For example I know that RSC Malaysia cannot provide full service warranty of the SeaDweller reference 1665 as the parts for the watch is very difficult to get. But this does not impact things like water resistance as they can change the gaskets etc, unless your case is damaged. It usually covers things like the bezel insert, dial or hands, more so if you insist to keep them original (tritium hour markers dial and hands).
There are other differences as well like the actual issuance of the service warranty certificate and if they give you the watch back in a Rolex service box or not.