It's important to remember that rats handle everything differently pending the individual, while some may not change regardless of raising litter after litter there are some females who become nervous or aggressive with lasting effects after birthing/raising their young. From start to finish pregnancy is a very hormonal and emotionally involved process. It really boils down to it if the Mother can actually handle all of the stress, hormones and the pups themselves. After seeing some great rats turn to utter messes after raising just one litter, it makes sense to say so. I used to have a great pet rat doe until she got loose into the bucks cages one day. After raising her litter (successfully) she just never was the same and isn't as friendly anymore. Shes rather a shutter bug now sadly. Of course there are those who breeze threw it like pie too. Again, all on the rat. So yes, it can POSSIBLY effect their personality permanently or long term in my opinion. It's not all that common for it to be severe/mild but it definitely happens. So choose wisely on what you want to do and keep in mind it only takes one baby or a bad litter to kill a Mom rat off too.