The hypo strain is capable of making the body of any creature increase in size
The hypo- prefix generally means below (eg. hypodermic) or reduced or deficient (eg. hypoxic). I'm not gonna tell you that you can't use whatever random cool-sounding bit of Greek and do whatever you like with it, but, y'know, words have meanings and not sticking to them is at best, a bit weird.
making it almost twice as big as it would have originally been.
Assuming a species with determinate growth (eg. they stop growing in adulthood) infection during adolescence could induce something like gigantism. Note that this comes with a whole raft of problematic side effects, health problems and usually results in death much sooner that would normally be expected.
It also allows for the body to heal wounds quickly, turning some would be fatal injuries into minor ones.
Everything already heals as quickly as it can, because being injured is obviously bad. Tradeoffs could perhaps be made... faster clotting at the risk of thrombosis, perhaps.
Another upside is that the host develops a thick armor plating around its body, which is hard enough to deflect some minor bullets.
I'm not sure what a minor bullet is, but I suppose it might be possible to induce growth of thicker bone and more leathery skin and (if applicable) chunkier scales... but all of that will come at a cost to flexibility and mobility. TANSTAAFL, and all that. Well armoured species have evolved an entire bodyplan to facilitate the growth of their armour, support its weight, and allow them sufficient mobility. You can't trivially encode all that in a little virus, and certainly not for a virus that affects multiple species.
One extreme downside to having this strain is that it causes the host to have a accelerated metabolism, which forces them into almost constantly needing to feed. This strain will also cause herbivore to turn into very aggressive versions of themselves, and will sometimes cause them to eat meat.
This seems just fine to me, and is about the most plausible thing in this whole idea.
Plenty of herbivores will already tuck into meat when it is available; they're not geared up for hunting, obviously, but scavenging is not out of the question.
Carcass consumption by domestic rabbits.
It also causes the body to change its towards more dull or dark reddish colors.
Sure, why not.
Could such a virus feasibly exist
Doubt it. We have a huge variety of species and viral strains on earth, and there's no indication that anything like this has existed. That said, a virus that induces aggression isn't unreasonable (rabies can do this) and weird congenital physiological changes are also not out of the question that might include gigantism and "armour" in children of infected animals. Developing those physical changes in an adult on the other hand, seems almost entirely implausible.
If not, could such a virus ever be created in a lab setting
Sufficiently advanced technology is of course indistinguishable from magic, so in that regard: sure, magic could do everything you want. It is magic, after all.
What seems more practical is to have a species that is already prone to these sorts of changes, and use a virus to trigger them. This still won't get you eg. massive growth in adulthood of a species with determinate growth limits, however, and a body which has developed without armour is likely to be hindered by its sudden appearance.