I can confirm that having used minoxidil for over five years I melted the foam into a liquid and applied it.
It made sense to me as applying liquid meant more went on the scalp.
Despite people being concerned it might not be as effective when melted, I proceeded anyway. I went from having almost no hair on top, to having a full head of hair within four months.
I continue to melt rogaine foam to this day and can confirm that melting it has no negative effect as that i regrew all my hair using the above method.
HLV