Would baffle dimension change of 2.5mm in all 4 sides change sound in a significant enough way?

[Franonymous]

If I applied 2.5mm thick veneers to the cabinet would it change the sound in any perceivable or measurable way? Speaker in question is travelers by Holtz and Campbell

 

[stv]

would it change the sound in any perceivable or measurable way?

I would say no.
You could try to compare the diffraction results using vituixcad or "the edge".

 

[mordikai]

I've found any adjustment less than 10% (maybe more) of the original has minimal effect, at least I can't hear it.

 

[Kev06]

It is possible that adding 2.5mm of veneer to the walls might slightly increase their rigidity and also change their resonance characteristics. But I strongly doubt you'd hear much difference unless the original walls were pretty flexible or light (e.g. foam-board).

The tiny dimensional change would (IMO) make no audible difference in a typical speaker cabinet.