Just in case

Make a copy of or load the original obj file into UVMapper Classic

In this demo I'm using a cube that has a material per face, group per face, and UV island per face. So that's 6 materials corresponding...

I want a template for the bottom right UV island corresponding to material6

I go to the edit menu and choose select by material.

There's no inverse selection option in UVMapper classic so I'll have to select everything but material 6... hold shift key to select all but 6

Everything but 6 is selected, highlighted red...

Your mouse cursor is now a translation/movement cursor when you hover over the islands. You can move the selected islands about the tile... but first press and hold the minus key. This will scale the selected islands down. Scale the selected islands down tiny and drag them off to the side of the tile...

Go to File menu and select Save Texture Map...

You can export your template as a bmp image. Choose the template resolution. Do not save changes when prompted. You don't want to change your UVs on the original model or save the original model out, just the modified template(Texture Map)...

Save the template out. Import it into your image editing software. Create a duplicate layer from the base layer into a new file or into the layer stack, marquee select the shrunken bits and fill with white to hide those bits if you want. You now have a template for the material6/group6/ UVIsland6 of the model. I sometimes select by color, select the black of the template lines with the eyedropper, and stroke a few pixels center of the resulting selection to give the template more pronounced lines. Just enough to emphasize but not so much to cause template inaccuracies of borders. I usually just generate my templates out of Mudbox these days though, UVMapper Classic gets confused by UDIM.