Change carbon content of energy carrier for different years

[demar]

Your problem appears to be a VEDA issue, and not TIMES.
I believe the VEDA ~COMEMI table generates TIMES VDA_EMCB attribute instances, but it is possible that VEDA does not support year indexes in COMEMI tables.

But the TIMES VDA_EMCB parameter does have a year index:
   VDA_EMCB(REG,ALLYEAR,COM,COM)  –  Combustion emission parameter

So, it should be easy to define year-specific values for it in TFM_INS / TFM_DINS tables. The first commodity is the source of emissions, and should be specified in CSet_CN. The second commodity is the emission commodity, and should be specified in Other_Indexes.  That should give you all the info for using it.  However, should you prefer to define it in a FI_T table, I think that would be equally easy.  VDA_EMCB is automatically inter-/extrapolated by TIMES, and so no IE option should be needed.

Do you mean with creating a scenario?

I tried, but it seems that the only value is assumed for the carbon content is the one I set in VT file (not specifying the year)