Psychedelics build up tolerance quickly. So doing shrooms two days in a row is likely to lead to a diminished or non-existant effect. You usually would have to space it out 3 days. What if instead you for example took shrooms on Saturday and Peyote on Sunday? Although both are psychedelics, each are different psychedelics. So wouldn't it not make a difference and will I have an equally strong trip with shrooms on Saturday and Peyote on Sunday?
You will build a quick tolerance to mescaline, but your right that it goes away relatively quickly, although not as quickly as LSD. I usually have to wait about 2 full weeks before I can get the total experience again with the same dosage. Since you'll be dealing in 2 different chemicals; Psilocybin and Mescaline, it doesn't sound like there will be any tolerance, but since it'll be hitting your body in similar ways there' could be. Best thing to do would be just to try it out - see how it goes - and report back