Commands:
<bool> = loadCustomProfileNamespace <string>
Unary command that loads custom profile namespace with name supplied as string. Target filename could be something like <profile>.<string>.vars.Arma3Profile in the profile directory. Returns load failure or success as boolean, true if name was provided, file exists and valid, false otherwise.

<bool> = saveCustomProfileNamespace
Saves currently loaded custom profile namespace that was previously loaded with load command. Return true if writing was successful, false otherwise (file is read only, custom profile namespace wasn't loaded, etc.)

<namespace> = customProfileNamespace
Returns currently loaded custom profile namespace variable to use in scripts. Null namespace if it wasn't loaded.

Additional twists to the idea:

• Define custom namespace name in description.ext instead of scripting command, something like customProfileNamespace = "my_mission";. Less flexible but maybe easier to implement in the engine.
• Save variables globally instead of to your current profile, so namespace is accessible regardless of selected profile, which I'd see as an upside. Commands could be named as loadCustomNamespace, saveCustomNamespace, customNamespace then.

Alternative command set approach idea
<namespace> = loadCustomProfileNamespace <string>
Loads namespace into variable.

saveCustomProfileNamespace <namespace>
Saves namespace onto the disk.