you can in slateport in hoenn and eterna in d/p i dont know for fr/lg
You Can Go By The Pokemon Name Rater
when you first catch a Pokemon you can give it a nickname but if you want to change its nickname then you need to go to slateport city and talk to the nickname rater (he will change the name of any of you Pokemon that are in your party)
You can go to the name rater in Lavender.
go to the tent in goldenrod
i think somwere in orebrough
Go to Eterna City and go into the building, that has the Name Rater on the sign. Talk to the old dude at the table and he will "rate" your pokemon's nickname and ask if you want to change it. You cannot change a traded pokemon's nickname.
Go to the house next to the Poke Mart in Eterna City. Talk to the old man and he will change your pokemon's nickname. Sadly, you cannot change the name of trade pokemon.
There is a man in Slateport that will change your pokemon's name.
When you are in Pokemon go look at the bottom left corner. Right by your experience bar and level will be your nickname for your account. If you don't see it try clicking your EXP bar to open your profile.
Do you mean nicknames for Pokemon? If so, simply nickname a Pokemon when it gives you the option to after catching it. If you wish to change or give a nickname to a Pokemon you caught before, go to the Name Rater in Eterna City. You cannot nickname Pokemon received in trades.
go to the city before mavlie city stateport
After you catch, hatch, or receive a Pokemon as a in-game gift, you'll be asked if you want to nickname the Pokemon. You can also nickname a Pokemon by going to the Name Rater; where it is depends on the game you're playing.