@phaselock : I see, from the images above, you are using Blender 2.8+, so here is a suggestion you may or may not find useful. Add a second material with a texture of some kind to your cube (or other mesh). This second material can have exactly the same parameters in Blender - just a different name.
When you look at the babylon file you will now see something like this:
“materials”:[
{“name”:“Cube_baked”,“id”:“Cube_baked”,“customType”:“BABYLON.StandardMaterial”,“backFaceCulling”:true,“checkReadyOnlyOnce”:false,“maxSimultaneousLights”:4,“specular”:[0.5,0.5,0.5],“specularPower”:76.8,“alpha”:1,“indexOfRefraction”:0.6897,
“diffuseTexture”:{“name”:“brick1024.jpg”,“level”:1,“hasAlpha”:false,“coordinatesMode”:0,“uOffset”:0,“vOffset”:0,“uScale”:1,“vScale”:1,“uAng”:0,“vAng”:0,“wAng”:0,“wrapU”:1,“wrapV”:1,“coordinatesIndex”:0}},
{“name”:“Material01”,“id”:“Material01”,“customType”:“BABYLON.StandardMaterial”,“backFaceCulling”:true,“checkReadyOnlyOnce”:false,“maxSimultaneousLights”:4,“specular”:[0.5,0.5,0.5],“specularPower”:64,“alpha”:1,“indexOfRefraction”:0.6897,
“diffuseTexture”:{“name”:“brick1024.jpg”,“level”:1,“hasAlpha”:false,“coordinatesMode”:0,“uOffset”:0,“vOffset”:0,“uScale”:1,“vScale”:1,“uAng”:0,“vAng”:0,“wAng”:0,“wrapU”:1,“wrapV”:1,“coordinatesIndex”:0}}],
“multiMaterials”:[{“name”:“testuvs01.Multimaterial#0”,“id”:“testuvs01.Multimaterial#0”,“materials”:[“Cube_baked”,“Material01”]}
],
Look at the code, and you will notice that it will allow you to play with u/v offsets, uv scales etc for both the different materials.
The image below was created that way, but after export, I then just changed the u/v scale in code for one of the materials (single face at the top).
Stay Safe, gryff 
