can I return back an Item for changing?

No. You can return it, then buy whatever you want to exchange it for.

You can return anything at any time. Except for electronics I think there's a three month policy for electronics

Cosco has an excellent return policy.

All Costco store's allow exchanges up to 3 months, but, as i understand it, you cannot return food items that have expired after your purchase date.

Yes

Costco accept returns or exchange upto 3months

Yes, you can do it,, changing or refund

I don't exactly understand your question but I assume you're asking that could you return something yes you can return and then rebuy the item