From what I know, the band was started in 1980, and it was considered that Pata was the leader of the group. The group disbanded in 1982, when all the members, except Pata, decided to give up music.
As for the name change, it could very well be because of Masayoshi's band. Both bands were active at the same time, although because Masayoshi is older, it can be assumed he started his band a couple of years before Pata's Black Rose. Masayoshi and his band, and eventually Loudness would be all be based out of Osaka, while Pata and his band were based out of Chiba, which are quite a distance apart. So it could be very possible Pata was unaware of the Osaka based Black Rose until after he started his own band under the same name. So too avoid confusion between the two, Pata might have decided to change the name. Similar to hide's band, when they changed their name from Saber Tiger, to Saver Tiger, to avoid confusion with a band of the same name from another part of Japan.
However, this is just a theory I came up with off the top of my head. None of this is proven fact as far as I know, and with Pata's quiet, and private going style, we'll probably never know.
