Here is the link to PhrozenKeep's
Hirelings Reference. Asking the question there (or maybe the homemade modifications forum) might get better answers.
As mentioned on PhrozenKeep, "Resist" receives a number that will become the merc's base resistances when they are at "Level". For example, in HUv1.7 I noticed Mercs resistances were too low in NM and Hell, so I decided that they needed to sort of benefit from the Anya quests's +10%ResAll buff. I have a row in hirelings.txt for each mercenary where at "Level" 80 their "Resist" is 10, and at "Level" 95 their "Resist" is 20. I think I recall a test where I leveled a Merc from 79 to 80 while looking at their stat screen and I saw them gain 10%Res upon leveling, but maybe I was confused and they simply killed a monster that was debuffing their resistances.
For every level the mercenary gains beyond "Level", their resistances would improve as in "Resist/Lvl" (Note this receives a number in 8ths, so use 16 if you wanted 2%ResAll/Lvl).
I think in your case, for a level 10 Rogue, you'd want "Level" 10, "Resist" 20, "Resist/Lvl" 16. For a level 70 Rogue, you'd want "Level" 70, "Resist" 140, "Resist/Lvl" 16.
I haven't done too much experimentation with Hirelings, so let me know if your experiences contradict what I wrote above, and I'll look into them again.