If you don’t mean Mekabel, don’t use the word. A Kabalah is like a Neder and it works the same. There is no such thing as making a Neder that you weren’t aware of.
The only similiarity to Kiddush and Sefira is the fact that you are using your mouth. I don’t think there is any case of being Mekabel anything without being aware of it.
You seem to be making another point here as well. You’re saying that if you make Kiddush Mibe’od Yom you are Mekabel Shabbos with that, and that saying Gut Shabbos on Shabbos can be considered Kiddush. So you make the connection and add them up and say that if so, saying Gut Shabbos on Erev Shabbos is also Kiddush and is therefore a Kabalah as well. But, you have to first proof , or perhaps show why it makes sense to say, that saying Gut Shabbos before Shabbos (which does not mean, and you don’t mean it to mean, that it is Shabbos) is Kiddush.