I’ve tried to change them too without result (values return to default after restart).
Anyway, there’s already a mod in the steam workshop that changes the dodge roll 's speed :
"Dodge Rebalance-Roll Tweak - Light Armor dodge roll speed increased from 1.6 to 2; - Medium Armor dodge roll speed increased from 1.23 to 1.5; - Heavy Armor dodge roll speed decreased from 1 to 0.85.