Adding and modifying parameters to present url

Hello,

I'm having problems creating a new link that points to the same
action, with the same existing params, but that would also add a param
or modify an existing one.

For example, I have:

http://www.mysite.com/search/results?string=ruby

I'd like to be able to create a new link that adds a new param:

http://www.mysite.com/search/results?string=ruby&page=2

Then modify an existing param:

http://www.mysite.com/search/results?string=ruby&page=3

Any help would be appreciated.

Thank you

Olivier Dupuis