Are there any ways to overcome a spells spell power cap?
For most of this run as a VpEn, Ensorcelled Hibernation has been my main single target spell of choice. However, it has a spell power cap of 56, which means that now that I'm in the Vaults, I have at best a 55% chance of it working, and sometimes much much less depending on enemy HD and MR.
Are there any ways to ignore or partially bypass the power cap for a spell or do I need to just switch to different spells? (I have discord castable already, but in a single target fight I don't want to frenzy my opponent)
You'll have to switch spells. While there are some tricks you can use to increase your success rate a bit (i.e. read a Scroll of Vulnerability), even those will not be enough. Also, Ensorcelled Hibernation is particularly bad because it has no effect on anything with cold resistance (which becomes rather common later on).