I don't have a Humax STB of any kind, but I have done some research into the subject and the following are my conclusions:-
The Humax HD Freesat box is supported by the PUC and can be uploaded by the dealer.
All the Humax remote infra-red signals I reviewed used NEC protocol with a carrier frequency of 38Khz
The following is the protocol used by all the Humax codes I reviewed
In particular, I compared common commands used by the Humax PR HD 1000 and the Freesat HD and I found them to be the same.
As an example I looked at the UP & DOWN commands and both had the following bit string:-
UP binary BITS=11111111 01101101 01110111 10001000
DOWN binary BITS=11111111 01101101 01010111 10101000
As you can see above all Humax STB's uses the same product address of FFB6
So, the conclusion is that for common commands, it will work, but you will find that there are a couple of FREESAT commands which will not be available.