Anything is possible, as long as you accept painfully slow speed.
The problem is that the slower the RPM the less is the torque, so in your case, I'd get a new 48V supply, or connect a 12V in series with the 36V to get maximum RPM. Perhaps you can find a 12V supply in your drawer...? Just make sure it has enough power.
I run my 24k spindle at 22k to reduce noise and I don't think it would make much difference if I'd run it at 24k.
https://youtu.be/nrW6Hq6V3VY
I am also using 30deg V bits and some drill bits made for PCB. You have to experiment optimal mill speed and plunge depth/speed. Yes, expect breaking V bits and drills until you get the feel. It is impossible to give good advice regarding speeds without knowing more about your machine. Milling speed depends on many other things, not only RPM. Yes, you should definitely modify your speeds, the reduction from 9k RPM to 7k is significant. Be careful when drilling, don't go too fast. On the other hand, if you go too slow, you'll burn the PCB and the drill...