How to change a default value in the run_card once and for all

Since 3.5.0, you should have two new files in the input directory:
 - input/default_run_card_lo.dat
 - input/default_run_card_lo.dat

By default, those files are empty but you can add entry into those files (with the run_card syntax).
Any entry with that file will overwrite the equivalent MG5_aMC default value of the run_card that we assign for your process.

For example by adding the line
 2 = dynamical_scale_choice
You will ensure that all generate directory will have as entry for the dynamical_scale_choice the value of "2" (HT)

Warning: When using such feature, you can obviously get default run_card for a given process which are not tuned for your process.
For example if you set in that file
" 1 = lpp1"
and then generate a code for e+ e- > mu+ mu-, then your code will return zero cross-section by default since the default run_card that will be generated will launch a computation where we convoluted the matrix-element with the PDF of finding an electron within the proton (and for the default pdf this is zero)