Would a stone be more powerful if you were to program it with your intentions on Halloween?
Overall I would say no, as it is more the intent rather than the time (it not being a full moon this Halloween). However, it may depend on what the stone is to be used for. Stone runes, stone pendulum, fairy stone (with hole in it) to see the fey, scrying stones and crystal balls, etc. These would be more reasonable objects to bless and program on Halloween, imo, since the history of Halloween is so rich with various kinds of divination.
Thank you very much HearthCricket. This is very helpful. I guess had a full moon or new moon fell on Halloween it would be different, but since there isn't one this year it isn't so significant.