For now ..... split your Imitrex injections. https://clusterbusters.org/forums/topic/2446-extending-imitrex/\ If I had to suggest one culprit for what's going on now, I'd look to the Imitrex, which famously makes attacks longer and more resistant to treatment, and lengthens cycles. Using less is better. Using none (eventually) is of course ideal.
It's very common for pharma things that worked in the past to not work anymore. The "medical" solution is more: higher doses of verap up to 960 and even higher; longer and stronger pred tapers (a leading CH expert recommends 21 days with multiple days at 60mg). As you have said, this might have short-term results but long-term drawbacks.
Oxygen doesn't go that way. It works and keeps on working. Same is true of the D3 regimen: https://clusterbusters.org/resource/d3-vitamin-therapy-and-loading-details/ Same is generally true of busting, with some adjustments required by some people. (Click on "New Users - Please Read Here First" in the blue banner near the top of each page.)
A "certificate of medical necessity" from your doctor seems to help with insurance approvals. As you might know, many people with CH (probably at least one in five) use welding oxygen, which can be obtained without a prescription. https://clusterbusters.org/forums/topic/5627-notes-about-welding-o2/
Try downing an energy shot (for example, 5-Hour Energy) at the first sign of an attack. You might get some aborts from that, which will reduce your Trex usage. (Strong cup of coffee works for some, other kinds of energy drinks, such as Red Bull or V-8 Energy, can also be effective. Despite their small size, energy shots pack the highest caffeine punch.
Check your triggers. You never know. https://clusterbusters.org/forums/topic/4568-triggers/