I've looked around and saw several topics about how Rex's Weakness works with elder sign (star) token if elder sign is drawn second.
If elder sign is drawn first and +2 is selected and the test would pass triggering Rex's Curse, would the +2 be applied from the elder sign as an effect, or would the +2 be considered a modifier and lost.
Rex's Curse
The +2 is indeed a modifier, so you would ignore it due to Rex's Curse.
If you have any more questions about how Rex and all his cards work maybe check this video out.
Hope it helps!