How can I change the URL to my form?

Regarding the second question, can I change a custom URL before it transfer to sknspausa@gmail.com? So I can use the custom URL too after transferring. 

You can create a custom URL to your form before they get transferred to the new target account, but they will not work once transferred since the account's owner will change, what I would suggest you is to change the custom links after moving the forms, this will generate the new link under the current username and you will not need to change them again.