Please improve the node user attribute REST API to be able to add/remove/change a subset of user attributes and preserve the values of the remaining attributes.

I don't want to always fetch the entire xml representation of the user attributes -> change the wanted attribute and send the entire xml representation back to the server. Also if someone changed another attribute which I didn't want to touch in the meantime (between fetching and sending the attributes) anyway it will be changed back to the value it had before.