In answer to your first question... yes. In certain circumstances you can use arithmetic to mimic logic in inline rolls. For instance, you could multiply your mod (-10) by the result of a mathematical operation that would render either a 0 or a 1. The idea would be to derive a number between 0 and 1.999999 and then apply a floor() function to that. You'd set up your math to generate something below 1 for when the mod should NOT be applied (0 - .99999 when passed through floor() becomes 0, and -10 * 0 = 0 mod applied), and something between 1 and 1.99999 for when the mod SHOULD be applied. As for what that math would have to look like, we'd need more information on how the game mechanic works. Does the fatigue bar count up (higher numbers mean more fatigue), or does it count down (the character is losing stamina)? Is there a max value available to the bar? Is the point where the mod would be applied a matter of a percentage against the bar, or is it a standard value across the board? Also, is there actually 2 mods (-10 and -20), and therefore 2 places where a value in the fatigue could drive a change in the mod being applied (ie, -10 for a character that is *this* fatigued, but -20 as that character passes *that* point of fatigue)? If you share more information someone should be able to help derive an equation to fit your needs. As to your second question, the only way to have different text is with a rollable table (which kills your ability to perform the above math-logic), or with mods.
