There is no ethical provider who is going to do this at this juncture. It would be pure medical experimentation with potentially deadly consequences.
Yes, but to a degree any physician who treats ME/CFS with anything besides GET and CBT is engaging in medical experimentation with potentially deadly consequences. The properly 'ethical' provider would wait until proper clinical trials are run on ME/CFS patients (which would also likely require proper diagnostic tests for ME/CFS to be developed). Then when the drug is approved by the FDA for ME/CFS, they could ethically rx it. Any provider who has rx'ed a drug off label is engaging in medical experimentation. And most of us desperately look for doctors like that because the alternative is to get nothing, or to get the easily received psychiatric diagnosis and be treated with a panoply of psych cocktails.
Personally, I think it depends on the justification. If someone has mast cell (unlikely to have a totally inactive immune system) and weighs 90 lbs, then a half dose might not be crazy or have deadly consequences. But yes, anything is a risk, INCLUDING getting vaccinated as performed in the trials as Judee and many others have sadly experienced.
Life is risks - hopefully we minimize them and make good choices. Some like myself are here because we listened to too many doctors who gave us the medically appropriate advice (push through, take some NSAIDs if you're in discomfort, don't worry about making things worse long term).