Ok! Lets hold the fluff wars for a 'sec. I'm gonna give some sugestons for some alternate background for the 40k lizards.
Long ago, in the late 38th milenum, a group of Imperial researchers investicating Warp irregularites in one of the more desolate regions of the galxey discovered a large habitable planet caled Plagiarius Lacerta.
The planet hosted a species of sentent "lizards" who had only pre industreal technology... ...but they had somthig else that deeply fighted the Impirum: Warp powered weaponreay from ancent times before Man.
So, the order was promply givin, and the destuction of Plagirius Lacerta was about to comence. The researchers were also ordered to obtain an number of living xeno specimens for experimentation.
It seemed that the entire culture and religon of the ailens were baced off of a apoticlipic proficy were the final end of Plagiarius Lacerta wad very, very nigh, and that they knew nothing of the ancent weapons and tecnology disgarded on their planet millions years ago by some unknown space-fairong race.
There was an apocolypes: the orbital bombardment of Plagiarius Lacerta.
Meanwhile, the researchers had discovered somthing intresting: a bacterieal in the xenos' bloud stream could be extracted to create a extreamly powerfull virus perfect for biological warfare.
Atlast, to test this virus, the needed ginney pigs. Humans from all over the galexey were broght in. Edventually, they descovered a problem. The bacterea was very simmilar in make-up and perpous to a bacterea in the Human body: D.N.A. As such, the test subjects begain to mutate, but usualy the body rejects the mutation and shuts down.
Howerver, some people, mostly young children begining puberty, proved to be extreamly receptive the drug and begain to sucessfully mutate untill human/lizard-alien. "Lizard Men"
Shootie Orks' combat guild:
Pull trigger in direction of enemy. Repeat until done.