Back when I got my very first metal miniatures (a box of Space Wolf Bloodclaws, back in 1990 or somewhere around that time), I did all my cutting with a Stanley knife, as that was the only thing I had available at the time. I had decided I wanted to convert this squad into Dark Angels (oh, the irony
), and therefore had to do a lot of cleaning up. Wolf tails, pelts and tassels all had to be removed and I did it all with that one (not too sharp) Stanley blade.
Over the years I became very adept at (re) sculpting metal miniatures, but as Wyrmala already mentioned; it took a lot of time and effort. but the results were good; I actually re sculpted a chest eagle on the sergeant of the above squad out of the bare metal of the mini!
But it was slow going, mildly dangerous (I have the scars to back up that claim), and not as detailed and fine as I'd have liked.
So I dug out the jeweler's saw I had to get when I started the academy of fine arts, but never much used. And that was my conversion work horse for decades. It's useful in the sense that you can create curving cuts following contours etc, but it will still only be a 2D curve; the blade has to be straight, and having too much slack on it, or too much laterar force (in either the Y or Z axis) will break it immediately.
And I've broken my share of blades over the years...
But late last year, I found a reasonably prized razor saw (by Tamiya) on Ebay and bought it. And for straight cuts, it simply cannot be beat! No curves are possible, but the cut is very thin, very straight and because of the size and shape of the blade, you can exert ample power to the blade without fear of snapping it too.
So that has been another welcome addition to my arsenal. I rarely dry-sculpt metal anymore, as these days, I will simply cut away too much and then sculpt it back in putty, but both the jeweler's saw and razor saw are used very frequently.
Blade types; there are all sorts, but I recommend getting the finer ones for soft metal, but basically any saw blade for cutting metal is ok. Just make sure you put them into the saw the right way, or you'll cut when pushing instead of pulling, which will not work at all.
Smaller teeth give more control over the cut and make it easier to curve and control. And because they're smaller, they will also pull out less material per stroke, and that means less force is required, leading to less breakage (but there will be plenty of snapped blades at first, be prepared for that...).
Don't worry about the blades filling up with metal; this can be pulled out/off easily, and I often do that by simply running my thumb along the blade, gently breaking off the pewter/lead. If you use them with plastics, it's a completely different game though, as plastic will melt, and if you stop sawing, the plastic will cool and harden again and the blade can get completely stuck, embedded in the plastic.
So it takes a bit of trial and error to find the right sawing speed to prevent melting the plastic (which obviously varies per plastic type). regarding the wearing out of blades; I've never had a blade last long enough for it to dull, so I really can't comment on that
As for the razor saw; just get one made for model making and you're good. Blades will not break (unless you really go berzerk with them) and the teeth are designed to make as smooth as possible a cut anyway, and I've used it on both metal and plastic without issue so far. It's too early to tell if prolonged cutting of pewter will dull the blade quickly, but there was a replacement blade included with mine, so it looks like the makers do expect them to wear out over time ...