As I will tend to do, I wrote my previous post on offering bullets to the Morrigan based on the blank face of the question, to wit: is it appropriate to offer bullets to the Morrigan at all? My answer being yes, if and only if your own relationship with Her suggests that it is appropriate. That answer applies equally to any offering to anyone. My essential position is that offerings are a facet of relationship between the devotee and the object of devotion, and that relationship should thus naturally dictate the offering.
That said, it has been brought to my attention that in the original context there was a rider on this question, which was: is it appropriate to offer bullets to the Morrigan on a shared altar? In that case the answer is (mostly) no, on two grounds. Both center on the fact of the shared altar being shared, and thus a community space. It’s not all about you and Them any more; it’s about you and Them and everyone else using the altar. There has to be an accord there, as there would have been at any public temple back in the day.
First, you need to know whether nonperishable offerings are welcome at all. How are they to be disposed of after the ritual or event is over? Are you just assuming the holders of the space are responsible for keeping the thing indefinitely or disposing of it in a respectful manner? Have they expressed willingness to accept this responsibility? If not, you’re only sort of making an offering and sort of littering.
Second, are you aware of what the keepers of shared space prefer to be used as offerings in their space? Ideally they should make this known, but when in doubt you should ask. Part of being an adult in community is showing a basic ability to honor the house rules of the house you’re visiting. Hospitality is a virtue of many of our cultures, and this is a piece of that.
In other words, if the Morrigan asks you to offer a bullet it should go on your private altar, not a public one unless you get the go-ahead from the keeper of the altar. Likewise, if you are holding a public space open for offerings it is smart to let people know what kinds of offerings are and or not invited there.