Step 1: Place textures within the map files (I'd suggest in a textures/ground/ folder where textures is in the same location that the map .i3d file is found)

Step 2: Open map's .i3d file in a text editor and search for "roller"

Step 3: There should be two results in the <File> section, replace the diffuse filename="wherever the current one is/groundType_rollerLines_diffuse.png"
with filename="textures/ground/groundType_rollerLines_diffuse.png" or filename="wherever you put the textures/groundType_rollerLines_diffuse.png"
do the same thing but for the normal file as well.

Step 4: Done, now your rollers will apply a smoothed looking texture rather than lines.