Can you merge more?

I have +10 merged Nowi. Im thinking about new build (brazen atk/def+atk/res sacred seal), but was thinking about using different nature.
Is there any restritions abot merging +10 units?
Ofc you dont get Nowi to +11, but I assume you can add +10 to new one and get Nowi+10 with desirable nautre.