say that you have a 128 bit (32*4) VLIW word. Can each 32 bit sub-word contain any operation (ADD,CALL,BRANCH,...) if there are no hazards or can each sub-word only specify one functional unit (so if the BRANCH functional unit doesn't get used, that sub-word becomes a NOP)?
Can each VLIW sub-instruction execute any instruction?
computer architecture
Usually, VLIW instruction sets dedicate bit fields to functional units  (not necessary multiples of bytes, or the same width for all units), and when some parts are unused, they are configured as NOPs.Of course, there are exceptions, sometimes execution units are coupled, or special configurations are provided for long immediates... There is no absolute rule.You should look at sample implementations, like the 48bits SHARC DSPs, or the ST200 family.