The reason the model is all white is:
You changed the name of the main folder. The p3d is still looking for the textures in the old folder despite the changes you made. To correct this, open up O2, select the whole weapon (press Crtl-A), and click Faces\Face Properties in the top bar. A new window will pop up. In the top of this new window, you will see several rows of information highlighted in blue. Each row should look something like this:
0 14 15 16 OldAddonName\Texture.paa
Click the top line in this blue shaded region, now only that line is highlighted. You will see at the bottom the path for the texture. It should look something like this:
OldAddonName\Texture.paa
Change this to:
NewAddonName\Texture.paa
Where OldAddonName is the name of the old addon folder, and NewAddonName is the name of the main folder where your weapon is
This will make the p3d look for the texture in your new addon folder. You can select multiple faces if they have the same texture! Otherwise you will have to change each face seperately. You will have to do this for each face that has a texture!
It is a lot of work, but it should fix the problem.