The top result for "x cum y" on Google:
"Many English speakers would be familiar with the construction 'X cum Y' (where X and Y are nouns) to designate something or someone with two different attributes that are combined , e.g. model-cum-actor or restaurant-cum-dining room. The word cum here comes from the Latin preposition meaning 'with' or 'together with'. [from] Sep 27, 2012"
I don't know if your particular bit of Latin looks as officious as one
would want a motto to, anyway. Might as well just do English?