blacklisted

Tricky situation. I have an offer with a firm that I'm 99% sure I'm going to accept. However, I have a super day lined up with another company that I don't want to completely rule out at this moment.

I'm just wondering though if I go through and accept the super day, can I cancel it if I go ahead and accept the offer before the super day takes place? Or, does canceling a super day mean I'll be perpetually blacklisted from the firm in question?

I'm sorry if this question is a little confusing.

Thanks!