If all load cases are linear, just Right Mouse on Model > Insert > Solution Combination. Then Add to set your coefficients for each basic case. You can then copy the Solution Combination and go into it to edit coefficients as required.
Am I correct it is not possible to input all the coefficients with one copypaste but they have to be copypasted one at time?
I have a list of coefficients (altogether >100 values) for different combinations which I got from other software.
The other way round this would be to set up all the combined load cases and use Parameters to input the factored loads to each. Parameters can be read in from your external data.