You are correct Charlie, any slicing software has the option to scale, however as you enlarge the quality is very much dependent upon the level of detail in the model
Here's what I do (and I'm only just about a beginner):
1. Find the size of the real thing and thereby what size it would be in 1/72.
2. Start a Tinkercad account and upload your stl file to it.
3. Tinkercad has the easiest method to measure the size of your 3d model.
4. Compare the actual size of the 3d model to the desired size of your 1/72 model, and then set up a ratio to find out by how much you have to enlarge or reduce your model.
5. Upload your file to Tinkercad again but at the first screen is the option to enlarge or reduce by a percentage.
6. Export the file as an stl.
The only reason I am suggesting Tinkercad is because it has the easiest method of measuring the model.
I think it would be great if they were all in, say, 1/72.
I have a handful of WW1 files, but they are all various sizes, and because my brain has mostly disappeared (and what little remains is made of porridge) I have made no progress on making them into 1/72.