Can i give creatures with unleash counters, if i didnt choose to unleash them when they entered the battlefield?
Yes you can, but if it has a +1/+1 counter on it, it can not block. Doesn't matter where it came from.
{Rakdos Cackler}
702.97a (http://imtgapp.com/forum/index.php?action=imtg;area=rule;number=702.97a): Unleash is a keyword that represents two static abilities. "Unleash" means "You may have this permanent enter the battlefield with an additional +1/+1 counter on it" and "This permanent can't block as long as it has a +1/+1 counter on it."
Thats what it seemed to say, thanks. What a shame