This is true but mods do not override transmuters. They’re still additive. Tested it on storm totem transmuter + conduit once. Not that it matters in this case cause the weapon doesn’t have any phys.
Edit: I just realized this. The wording on the game guide makes some people think skill mod conversion happens before transmuters. But it literally states conversion on the skill or transmuter, meaning what the game guide actually says is:
Base skill (what’s in the skill itself) > skill modifiers (meaning all the damage and other stuff skill mods and item mods add i.e. crit, cc, everything that isn’t conversion) > conversion on the skill or transmuter (this refers to both item mod and transmuter conversions, meaning mod and transmuter conversions are additive) > Conversion on equipment and buffs (global conversion) > Equipment, Auras and Passives (This is where global bonuses apply)
That statement from the game guide explains conversion mechanics perfectly, including what damage bonuses converted damage gets, but excluding the interaction between single element and tri element conversions.