My posset curdled, is it salvageable?
Assuming that you are making a modern yolkless posset like this one: https://www.cooksillustrated.com/articles/173-introducing-lemon-posset 

This kind of recipe is very dependent on the ingredients ratio and the acidity. You have to pick a recipe which has sufficient fat (and you cannot substitute anything - use real dairy cream, not any kind of nut milk) and sufficient sugar to withstand the curdling. Also, you cannot have too much acidity - so pick a ripe lemon, and be sure to measure properly. If you have either not enough buffers (fat and sugar) or happen to have an extraordinarily sour lemon, you will get curdling. 

The recipe I linked also suggests partly evaporating the cream, which will be further help against curdling, but it should work without it too. 

It is impossible to change anything about the curdled dessert. You can either choose to enjoy it as it is (try thinking of it as a dessert on a tvorog basis) or toss it. You can also try dressing it up (add fruit or marmalade) or incorporating it somewhere (e.g. add rum raisins and use as strudel filling) but you will not get rid of the texture, so if you hate it, be aware you might waste more ingredients and still not like the result enough to eat it.