B - G to E - C tuning

The slots in the nut will be oversized. The nut will be fine as long as you remember to keep good down pressure at the tuners (wrap strings toward the headstock) and create witness points on the inside of the nut and saddles. If that is something that will bother you, you can have a new nut fitted to the instrument with the slots tailored to the string gauges you like.

Go online to buy singles or, better yet, have your local brick and mortar store order some for you. Then add the C string to a four string set. Or you can buy six string sets and collect/sell the B strings.

You should plan to do a set up. It may or may need to have it done. But plan on it.

 

YMMV, but from my sample size = 1, I did not have to change the nut when I converted my BEADG 5-string to EADGC. Just minor tweaks of the trussrod and the bridge saddles.

 

You certainly can try it with the original nut but if you want to get the best of the bass I would put a new nut on after deciding a wanted to keep it that way.

 

Bonus points if we're dealing with a zero-fret.

Riis

 

The Ibanez BTB845V "Solo" comes that way: E-C, 33-inch scale. I did the opposite: I bought it because I wanted a 33-inch scale, and had my luthier change the nut to "conventional" B-G tuning.

 

Truss rod adjustment, saddle height and intonation will need to be set, but I think the nut would be secondary. If you were going the other way and putting strings on that were too fat for the slots that would be a problem. It is possible that you may find the slots are not the ideal height though. Try it and see! Sounds like a cool idea.