Success could depend on your pimento cheese. Mayonnaise does not freeze well, it can separate. If your P cheese contains mayo, the texture could be affected. The taste will remain stable but appearance might change. Try it and get back to us with your results, please.
If freezing just the spread/pimento cheese itself, it should hold up well if wrapped in air tight plastic and then bagged.
If you want to freeze a whole or partial sandwich, bread can often be an "iffy" component with a non predictable outcome when thawed.
If freezing a whole or partial sandwich, I'd thaw in the fridge and then pan fry on both sides in a dab of butter or olive oil prior to consuming to crisp up the bread.
Other option is to reuse the hot pocket microwave sleeves.
Bread freezes adequately on it's own. When moisture or a filling is introduced, if not flash frozen at really low temps, the outcome is unpredictable.