By strict RAW, no.
But I would allow it.
There seems to be nothing on paper that indicates either way
My instinct would say no since the engraving of essential runes is mentioned within the discription of the keepsake as a specific thing that can be done which might not be valid otherwise
My feeling as gm says: go for it, talismans are not that big of a deal anyway and some on a case by case basis might be incompatible or just dont work by default
In the end its the decision of whatever gm you are playing with
I agree RAW no. But I also agree there's no balance reason to forbid to add talisman to keepsake. It's the opposite, this would make a keepsake worse than a Handwraps of Mighty Blows without any good reason.