Can I re-size photos before printing, and how?

Yes, if you do it from inside the Photos Library.

1 - selects the photo you want to print.

2 - in the edit mode crop it to the size aspect ratio (but as large as possible) you intend to print.

3 - select the resulting edited photo and use the key combination of ⌘+P.

4 - then do what's in this screenshot:

What do you mean by resize? Do you mean crop? If crop then yes, you can crop before printing.

You can resize file size (less only) during export. You can also resize the image size (less only) during export.

What system and Photos versions are you using?

Again, is this inside Photos?

Print your own photos in Photos on Mac - Apple Support

Can you give us an example? How are you printing, from within Photos? If so, Photos lets you set the size to print, ignoring any embedded dpi.