Reddit mentions of MAKOTO Handmade Sharp Samurai Shirasaya Sword …

> able to have its sheath replaced

Yes.

> and it's hilt remade into a traditional katana

Maybe. It depends on what the tang is like. It is certainly possible to have a new hilt made that looks like a traditional katana hilt.

But either of these would cost much more than the value of the sword if you were get it done professionally. It would be cheaper to just buy a new katana. Something that's better than this, either before or after restoration, could be had for under US$100.

> what type of katana this is

It's a fantasy katana.

The plain hilt and scabbard without guard or the usual fittings that strengthen the hilt and scabbard (hilt: fuchi (ferrule), kashira (pommel cap), and rayskin and cord wrapping; scabbard: koiguchi (scabbard mouth) and kojiri (scabbard foot)) is based on the Japanese shirasaya, a plain wooden scabbard and hilt for storage. A sword blade is put in shirasaya for storage, not to be used. But "shirasaya" is used describe plain no-fittings mountings for various swords, even if they are made to be usable. This is a mis-usage of the Japanese term.

Katana and similar with a forward-curved hilt are often called "jintachi". This is Japanese for "battle sword", and in Japanese refers to a sword suspended from the belt like a tachi (but would also include short swords and odachi worn like this, as well as normal tachi). For some reason (some anime?), this term was appropriated for these forward-curved hilts.

Combining these mis-uses of Japanese terminology, this sword would be a "shirasaya jintachi".

Real shirasaya: https://commons.wikimedia.org/wiki/File:Wakizashi_2.JPG

"Shirasaya" made for use: https://www.amazon.com/MAKOTO-Handmade-Sharp-Samurai-Shirasaya/dp/B07PHV8THX (note fittings to reinforce hilt and scabbard)

"Jintachi": https://www.swordsoftheeast.com/handmadesamuraisword66.aspx

"Shirasaya jintachi": https://www.swordsoftheeast.com/blackshirasayasword.aspx