Ah I see. Yeah, my confusion was mostly related to how it changes the attribute spread compared to other characters, where the sum ends up being +3. So I wasn't sure if it should also sum up to +3 (Str +3, Tough +3, Any attribute except weird -3) or something else.
Currently how I'm doing it is that it reduces one random attribute (except str, tough or weird) by -3 and increases Str and Tough to +3, but that can lead to an attribute spread that's very different from other characters (e.g. Weird +2, Str +3, Tough +3, Int -3), so I'm still thinking if that's the way to go.
Thanks for the response, glad to hear you're taking a look into it! Just out of curiosity, have you decided if you're keeping the option for trog PCs as one of the package deals?