Interrupter/suicide/safety levers add-on

yes you can. might as well rewrap and put new cables on

In theory yes. However, would you really want to install something labeled suicide levers?
Some models had the tendency to break or crack, thus the name. And the lever that sits closer to the handlebars tend to have much less breaking power. So it would only work properly at low ish speeds in urban areas. The normal break lever part on these work fine though

Technically yes, you can. But they will be a downgrade in several ways. I think some people even say they’re dangerous?

I would upgrade instead, to a pair of [Tektro RL-R340](https://tektro.com/en/product/95) levers (for comfort) and a set of cross top levers like the Tektro RL721. This setup will allow you to brake from the hoods and the tops if that’s what you’re looking to do.

You could also put some flat bars and levers on there if you aren’t into using the drop bars.

EDIT: the Tektro RL721 levers are for a 31.8 clamp it turns out, but you can use that as an example to find some for the smaller bars if they exist. I think it’s actually the [RL720](https://velo-orange.com/products/tektro-rl720-cross-levers-all-silver).