Can I use a pressure canner to can the cucumber jelly recipe or will it ruin it?

I can't say about the pectin- because I've never made cucumber jelly. I assume you have a recipe already, and that should tell you which type pectin to use, as well as let you figure out the ratios. You don't need to pressure can jelly, though. You can use the pressure canner like a water bath canner, simply by leaving the lid off. You just need to have the jar tops covered by at least one inch of water. Any tall pot will work, like a stockpot, so long as it is deep enough to hold water to cover the lids by the 1 inch.