How do I draw lines at work I won't cross?

You have done the hard thing: you know your lines and you choose your work by them. That clarity is rare and it costs you options, which is exactly why it is worth something. A line that costs nothing was never really a line. The ongoing test is to hold your principles without hardening into pride or rigidity. Stay clear about what you will not cross, but stay humble enough to keep examining whether a line still serves you or has just become a habit. Values are meant to guide a life, not to become a cage you defend out of stubbornness. Keep choosing by what you believe, and every so often revisit the lines to be sure they still ring true. The goal is not to be the person with the most rules. It is to live and work as someone you respect. You are already doing that. Protect it, keep it honest, and let it keep shaping the work you say yes to.