Equalizers do not have any effect on vibrato. As you said, it only allows you to selectively enhance or reduce specific frequencies of the sound you’re listening to. So if you set your eq to a sine wave pattern, it will just cut off and increase frequency bands alternately across the spectrum. So it will enhance and reduce the bass frequency at different points, same as with the mids and highs. In the end you’ll get a fairly flat response with some missing tones throughout.

It will change the intensity of specific frequencies.

Edit: are you talking about a specific type of EQ or the general concept?

Edit: to expand a little, the “bass boost” that was on countless music players for decades is an on-off switch for a specific, built-in, EQ curve with the low end increasing in amplitude (volume).

Or are you modulating parameters of an EQ? With an LFO for example.

If you listened to a tone rising in frequency, it would sound like a ducking filter (dependent upon the rate at which the frequency increased).

If you listened to actual music, which is not a rising frequency but a mixture of many different frequencies all at once, it would “hide” certain parts of the music and emphasize others.