The absolute easiest way is to "duplicate" the resources in a region,
one on top of another just increases the income without anyone knowing.
at the top of the descr_strat :
This will triple the income in marbletrade in abydus.
Code:
; >>>> start of resources section <<<<
resource fish 104 321 ;Aberdeen
resource marble 281 148 ;Abydus
resource marble 281 148 ;Abydus
resource marble 281 148 ;Abydus
resource grain 283 145 ;Abydus
resource fish 361 106 ;Acre
resource grain 349 135 ;Adana
resource silver 356 141 ;Adana