I have some rose must and it fermented too dry. I want to add
sweetness. And at 10 ABV a couple points of alcohol would be good too.
What should I add? Sugar? Simple syrup? Some wine additive? Any
ideas?

Thanks,

CAS

There is time to change the character of the wine you've built, all the
way up until bottling. Once you've taken the wine off your second
secondary, stabilize it with sorbate so there is no risk that
sweetening additions will ferment down the road. Then you can add
anything you like: simple syrup, wine conditioner, sweetened juices,
grape concentrate, honey (the latter three would require clarifying
later).

Fortifying with alcohol is done in port making for example. Add a bit
of Everclear (190 proof) using the pearson square to calculate the
required amount but don't let a winemaking purist know you've done it.

http://prechel.net/formula/pearson.htm

Good luck,

Jim