Disassembling Duplo push along train bases and car chassis

[Laltr]

Hi

Wondering if anyone knows if it's possible to (either) open up  a Duplo push along train (or) remove a pair of wheels by separating them from their metal rod? 

Also could do with knowing if it's possible to separate the drive rod from the wheel it's attached to. 

It's this type of base: https://www.bricklink.com/v2/catalog/catalogitem.page?P=4580c07#T=S&O={}

Reason is, I'm putting together a collection of adapted trains and need to swap colours around! 

Thanks for any help! I'll post pictures of what I've got so far if anyone is interested...