Interesting find there.
As other have pointed out, figuring out what the filler is will be key to determining if the thing can be deactivated safely or not (assuming that it isn't already). Your typical police and/or military EOD guys will NOT be trained, or equipped to perform such a task, these days they are pretty much taught to blow this stuff up rather than to fiddle with it.
IF it is a live shell, you are essentially looking at a glorified hand grenade, with the associated danger. Probably not much danger unless you drop it, toss it in a fire, shoot it, or drive over it with a truck.
Picric acid is rather nasty stuff, that was used extensively in WW1 and WW2 as a filler in small caliber artillery, mortar bomb, hand grenades, mines etc... As well as a "booster" (sometimes you need quite a bang to set off a large piece, so the blasting cap/fuze/detonator/whatchamacallit sets off a small charge known as a "booster" which in turns sets off tyhe main charge. The stuff <may> be in use to this day for all I know.
The problem of course is that it is an acid (even though it is a solid, and not a liquid like the acids you probably played around with in high school), which tends to want to eat up the bare metal that the shell consists of and produce salts known as picrates.
While picric acid itself is <somewhat> stable ("sensitive" to flame and shock), picrates aren't, and have been known to be EXTREMELY sensitive to friction, which is why just trying to unsrew the fuze is a bad idea.