Can I just paint textured walls that have been coated in smoke??

No you will have to wash the walls down with a vinegar and water 50/50 solution and allow to completely dry first. Use a good stain blocking primer as well.

I would wash walls with sugar soap before painting

Use TSP to wash the walls. If you don't wash them, you will have to use a primer as the nicotine will bleed through your paint. That is, if the smoke was from cigarettes. If it was from a fire, the walls still need to be washed with TSP as fire smoke can be greasy. TSP can be found in the paint department of a big box hardware store.

Hello. Before you paint I would clean the walls with TSP, and prime.

I agree with Claire

you are stuck washing the walls. nicotine will bleed thru the paint. get a clean sponge for the mop and gloves for your hands. nicotine can be absorbed by the skin.

Use Kilz paint. It's made to cover smoke and stains.

Good luck!