My fiesta struggled with emissions since it's not driven much and tends to short trip a lot too.
Emissions was high at mot time till I got in the driver's seat and held engine at 5k rpm for just over a minute solid. Could see on the machine Instantly the point where the cat ignited and emissions tanked right down and passed easily.
Everyone said I needed a cat, nop genuine one always gets the job done.
I'd be bit Sus if they want to take your Celica cat. It's gonna be worth more than any aftermarket replacement they put on. Make sure u get the genuine one back,
Although these days I think cat value has dropped big time, can't remember the last time I heard about cat theft