If you plan to keep the bike, on a limited budget, vs your timely repair expectation....
Option 1) Remove the existing bleed fitting's housing and repair the seized bleed bolt. Lowest cost if you can re-use the bleed bolt. Nothing to lose.
Option 2) Purchase a used housing. Rolling the dice a little but most used parts vendors offer a return policy in case the bleed bolt is again seized. Worth a try.
Option 3) Purchase a vacuum coolant filler (assumes you have an air compressor). Frankly, the best method to fill automotive coolant systems, period. However, you would need to ensure that the tool you purchase has a sufficiently sized filler adaptor. See link below for an illustration of such a device.
Option 4) Purchase a new housing. After replacement it's one less thing to worry about giving further trouble.
Weigh the above with the expenditure in the order 1-4 versus replacing an overheated engine or, at best, replacing the head gasket and the relative cost of the above.
The real key here is to do it once and do it as correctly as possible. Being too cheap can get very expensive
IMHO, there's nothing worse than the dread feeling that one's moved a bike away from a place one could repair it very well to a place that strands one on the side of the road with very limited repair capability.