Adding vendor specific TLV's for mBlox with unknown length

Hi all,

I am trying to add a couple of vendor specific tags, for the carrier 
mblox. The first two tags they have defined, have a length of 5. The 
other tags have a variable length.

Now I think when I change smpp_pdu.def I have to give the length as 
second parameter? For example:

TLV_OCTETS(mblox_session_id, 0, ?)

Problem is that, according to the specs, the length is variable. Now 
what can I fill in as second argument?

Also, just to make sure, I think I only have to alter submit_sm and 
deliver_sm. Is that correct?

Thanks in advance.

Kind regards,
Roland.