Hi,
I don't think this is possible, sadly. I asked if it could be implemented for the older 3D box in 098.9, but there were no takers. I had a play with the latest version and the 3D object last night, but I couldn't see anything to load/change textures, unless I'm just being dense. Hopefully it'll be available for this one. Either would save me literally 30 or so hours of work
Still, it's great to see the 3D aspects of Construct. A perfect excuse to learn some complicated maths and show a little creativity
*cough* If anyone feels that they could add the option to load textures to the old 3D box in 098.9 and it wouldn't be too difficult or time consuming, we'll credit you and throw you a few quid, as well as being eternally grateful *cough*