Adding a Domain to Channeler of the Unknown

[Andrew]

The Channeler of the Unkown archetype has a restricted list of domains. For my current campaign I want to add one to the list . I think I have found out how to do so but I cannot copy the archetype and produce a new version with the extra domain.
At the moment I can see 2 options
1)Manually copy the entire archetype into a new one , and then add the new domain
2) Overwrite the Destruction domain with the new one I have created , but this will change the domain for all characters .

As all I want to do is add one item to a list number 1 adds a lot of work , and number 2 looks dangerous.

The change I have made is to change the spells granted by the destruction domain at levels 3 and 8 as for this specific character 2 other options seemed more appropriate