As much as I'd hate to drop the default system, if I had to, I could always use D6, since that is now free. It even had a dice pool/count successes type system (think it was called D6 Legends?) that works similar to Storyteller.
Well, mechanics can't be copyrighted. The point is what you want to change. It may not be so "retroclone" anymore.
D6 Legends exists the way you said. You may go with it to achieve similar results a d10 pool system has. You can change a d10 pool system to make it differently. I don't mind using d12 or whatever. I can't say if it is easy to find but you can improvise it. Also it will be a system for a target public, due the effort of learning manual of techniques etc.
AFIK, the Opening the Darkness is OGL. It can't be undone. Author dropped since he disliked how it was portrayed by other people. It wasn't caused by directly White Wolf interference.
You can go with OtD and build a setting different from SF. The point would be balancing all new techniques. There is a lot of fan-material adapting SF:RPG for another video games in Portuguese, which is inspiring but at same time limiting.
I started worked in a fighting game but it never growth. The idea was: You have Strength 3, Punch 4, you can chose to roll just three dices (pick 2 Strength and Punch 1) to throw a job.
Bad results can turns into disadvantages. It worsen your speed, can turn into a special problem if another specific techniques hits you. Whatever that way.
You may not be totally free. Let's say you should learn specific techniques, with described outcomes and advantages for the poll of rolls.
I was more interested in building a fast-play with future supplements to adjust techniques balance. SF:RPG isn't exactly balanced and you need a lot of dices. Not always a problem; it's the flavor of the original system.
Spins can help to build an original work. However it seems more a modern design than a retro-clone.
TL;DR: No reason to be afraid, IMO. There are cool alternatives. The language of fighting video games and real martial arts may help building new setting, different maneuver names and stuff.