If Boo was released at half power...

[SSJ2]

Would he really have been unable to access all of his strength? His rage seemed to power him up without limit, and I can't see that not being the case if he was released at half power.

 

[Papasmurf]

He might have needed to eat a lot of candy or something. Kaioshit definitely believed Boo would be weaker if he were released at half strength. I don't believe he'd be unable to power up to his original level though, or severely weakened like the Homunculi in FMA.