Stat Changes
It seems very clear that you apply no stat changes.
This ability functions as a polymorph spell, the type of which is listed in the creature's description, but the creature does not adjust its ability scores (although it gains any other abilities of the creature it mimics).
There are no qualifiers here -- it says the creature does not adjust its ability scores, so it doesn't! The part of polymorph that you're looking at says that you
adjust its ability scores to one of these two sizes using the following table
This is exactly what the change self ability tells you to ignore.
Even though it doesn't use the word "adjustment" in the actual text of alter self, the word would generally mean any change to your stats. (And it would be a bit weird if shifting into a smaller form increased the strength of a Titan.)
Other abilities
There's nothing here to modify how polymorph spells work:
While under the effects of a polymorph spell, you lose all extraordinary and supernatural abilities that depend on your original form
Note the qualifier. You only lose the ability if it was contingent on your original form. In many places the DM will have to make a judgement call on whether that applies. But obviously, say, a manticore that shifts into human form can no longer use its Spikes special ability. The rule is intended to rule out nonsensical situations, so the change shape ability doesn't alter these rules at all.
You're confusing two different game concepts, which is understandable considering someone made the mistake of giving two completely different things very similar names.
Breaking it down:
- The Race you choose has Racial Traits. You get all of these automatically, just like you're thinking of. You pick a dwarf? You get all the dwarf racial traits. The "Gaining Traits" thing you found has no relation to these.
- Then the Advanced Player's Guide introduced a thing called the Trait system, which you can read about there. This is what the "Gaining Traits" thing applies to. These are optional mechanical bits you pick up for your characters. These traits are sorted into various lists, like Combat Traits and Equipment Traits. To confuse matters even further, one of these lists is also called Race Traits, which are so called because they always have a particular race for a prerequisite.
The racial traits from #1 have no relation at all to the traits system and race traits from #2.
The traits from the Trait system (#2) are like flavourful mini-feats you pick at character creation and which might reflect your character's personality or background (or you can ignore that bit). It lets you pick up neat features like an iron liver or an aptness at being a tactician. The Trait system is optional and your group can ignore it entirely.
Best Answer
A creature brews any fleshgrafting poison at the GM's discretion
The feat Brew Fleshcrafting Poison comes from Endless Night, the fourth chapter of the Second Darkness adventure path for Dungeons and Dragons 3.5 (that's what OGL after the path's entry on the Paizo Web site means). The feat's included on the d20PFSRD site, but it's unavailable on Paizo's SRD. Ask the GM whether material that was intended for D&D 3.5 (which is nominally Pathfinder compatible) is allowed in the campaign.
If the feat is allowed, one should then consult Endless Night and its (presumably closed content) descriptions of fleshgrafting poisons: antennae, blinding spittle, burrowing claws, chitinous skin, poison fangs, retractable spines, and stinging tail. (Tip: Some are okay.) One should also keep in mind that as of this writing there have been no additional fleshgrafting poisons in any other product.
Those fleshgrafting poisons that are described are specific yet don't mention actual creatures (for example, the antennae says, "You sprout antennae from your eye sockets, gaining blindsight out to a range of 30 ft. and normal (human-level) vision" (63) rather than, for example, "You sprout antennae like a rust monster"). Further, each poison has a corresponding penalty while the poison's in effect (for example, for the antennae the penalty is −2 hp per HD). (They are, after all, feshcrafting poisons.)
In short, trying to divine how to use the feat Brew Fleshgrafting Poison solely from the information provided by the d20PFSRD is a frustrating and ultimately fruitless exercise.
Thus, for example, were I the GM I would look askance at a player who tried to convince me, as posited by this Reddit thread, that a creature can use the feat Brew Fleshgrafting Poison to create a magic item costing 2,000 gp that forever grants the imbiber the dwoemercat cub's supernatural ability dweomer leap... especially if the player hadn't consulted the feat's source (which describes in greater detail the effects of chugging a fleshcrafting poison) and argues that there should be no side effect (as each and every printed fleshgrafting poison has one).
In other words, like some other niche item creation feats, the player should first have the full text of the feat—including the items the game already says the creator can create using the feat—and know how those items function, then the player can consult with the GM about adding new items to the extant list. (Then the creator and the GM can thumb wrestle over pricing by first comparing the new item to similar existing items, as always.)