Hello

I will be heading to Germany in a month and I will be doing a bit of shopping.

However, I will be flying from HAM to FRA with LH, and FRA-HKG with SQ.
I have asked LH and they allow a through check in my bags to HKG, but they wouldn't be able to print the SQ FRA-HKG boarding pass. Meaning if I have to get my custom stamps, it has to done in HAM.

So my questions are,
1) I am able to self print a FRA-HKG boarding pass, but will the custom accept it?
2) if not, without the FRA-HKG boarding pass, will I be able to obtain custom stamp at HAM for the tax refund?

thank you in advance