From The x3270 Wiki

wx3270 does not implement resources directly. Instead, it saves settings in profiles, and manipulates the resources in the copy of b3270 that it runs.

b3270 resources can be modified at the wx3270> prompt or from a script with the Set() action or Toggle() action. Changed resources are automatically stored in the current wx3270 profile.

Note that there is no way in wx3270 to change a resource that is not run-time settable. This will be corrected over time by adding this capability to additional resource types.