create minecraft/mcpatcher/cit folders
put inside that a .properties (text file that you saved as a .properties)
and name it the wway you want it to (ex: ruby_sword.properties)
put inside
type=item
items=minecraft:diamond_sword
nbt.display.Name=iregex:.*Ruby.*
# "regex:" is case-sensitive, "iregex:" is not.
# .* calls for wildcard.
#So for example, "iregex:.*Ruby.*" will search for any item name containing the word "Ruby"
texture=ruby_sword
And create a texture named (in that case) ruby_sword