"Zmieniłem się dla ciebie."

Translation: I have changed for you.

[Szymon.U]

not a good idea in the relationship :-)

[Euhan1]

So at least you're not wearing a soiled nappy...

[Paragonium]

Nigdy się nie zmień dla inni ludzie.

[Jellei]

dla takes Genitive, so "dla innych ludzi". And if you "never do that", that should usually take imperfective. So "Nigdy się nie zmieniaj".

I think that maybe there are some contexts when "Nigdy się nie zmień" would sound okay, but generally imperfective is the right way.

[Paragonium]

Thank you for pointing that out, Jellei. I should've known the change for 'dla', this slipped my mind. And that nuance of zmienić/zmieniać is quite useful.

[HippieRas]

Where can I find these rules?

[Jellei]

Try this post: https://www.duolingo.com/comment/16296174

[Glen624972]

Does this refer to a change in behavior/personality and/or a change of clothing (my wife didn't like my shirt)?

[alik1989]

Personality. I got changed for you would be "Przebrałem się dla ciebie."

[va-diim]

Russian: Ja izmienilsja dla tiebia. Fascinating!

[ada857852]

Jaki beta.