When saving a tree with a differnet name, the SmartMatches are NOT saved!!!! It would save MONTHS of work if that would be done. If I want to publish my NEW tree (saved with another name) and the SmartMatches were also saved I didn´t have to confirm ALL former matches again. In my tree it is about 100 000 matshes thas are lost.
You are right in that if you use the "save as" function in FTB, you create a new project with a new ID. When this project is later published to the MyHeritage site, it will be treated as a new tree and new Smart Matches will be calculated for it.
A possible workaround for your problem is to use the "rename" function instead. Go to File > Close project, and then to File > Manage Trees. In this menu you will be able to rename your tree without changing its ID.