[Snowf0x]

Is it possible to redirect to a different url when clicking Checkout (trying to buy) instead of the original /checkout/ page?
If yes, how?

[Jdxo]

You can do it in multiple ways..

add a 301(Permanent) redirect in .htaccess
get a wordpress redirect plugin. (I think there is one literally called "Redirect")
Add in some PHP code to change the link depending whatever state you are trying to manage (logged in/out etc).

If you have no coding knowledge just try looking for that Redirect plugin and it should be straight forward to setup and use.