I'm a recent PhD student who specialized in field X and have a couple options open in this field for my work. I like the field and it is field with opportunities in academia and industry.
That said, field Y is a passion of mine, it's very different and wouldn't have many skill crossovers. There is a job that has opened up for it that seems perfect for me. I'd love to contribute in the field and I could live off of it, but it wouldn't fit my field. I don't think I could easily find a another job in that field or move up really down the line.
My question is, can I have my cake and eat it too? Is it reasonable to take a job in new field Y and ask the employer if I can collaborate and contribute to field X still? If I have a break in my history of working at it can I get back into it without many (any?) publications?