During (overnight) Shmira for a niftar/nifteret (that is not a relative), aside from saying Tehillim, am I allowed to 'learn' for the benefit of the deceased, as long as I specify that I am learning for the zechut of Ploni ben Ploni?
Answer:
This is fine. Learning on behalf of the deceased is a zechus, as we know from the common custom of studying Mishnayot.
Tehillim are generally recited as prayer for the niftar's protection and merit, but Torah study is of course a blessing and a zechus, it doing so is fine.
Best wishes.