I have a much larger Becker's
Nevus that covers my entire left shoulder. I also have the same desire to tattoo over it as it is unsightly. I recently met with a
dermatologist, who was the first person to tell me that it was a Becker's mole - I'm 27 - and I asked her about tattooing over it. She said that there really shouldn't be any problem. Yes, generally you do not want to get tattoos over
moles as you can't determine any changes in pigmentation (obviously gotta watch for them to darken), but our Becker's is pretty rare and from what I've researched, I haven't heard anything about them becoming cancerous or even troublesome.
My recommendation - since yours is small, go for it. The trick will be convincing your tattoo artist that that's ok. Ask the tattoo artist if they've ever done anything like that. I'd also say visit with a dermatologist about it, too. See if he/she says the same thing that mine said.
I'm planning on trying
laser hair removal first. My dermatologist says it's pretty unsuccessful but to me it's worth a try. I'm tired of shaving my shoulder :/ Once I give that a go, I'll be looking to tattoo over it, but since mine covers my whole shoulder, I think what I'm going to do is have my bicep area tattooed with it covering just the edges of my Becker's. I'll see how that goes, then if it responds well, I'll go for the whole coverage. I'll check back with you. All the best!