Is there other ways of gaining an inhered template other then being born with it?
I have an idea for a creature that was sent to the plane of shadow from the material plane as a punishment. While the creature not only survives but thrives. So I was gonna give him the shadow creature and Shadow Lord template when he comes back home as a sub boss. The issue is getting over the inhered template as it messes with the whole backstory of character.
As a GM you\re not bound by such triffles, you're allowed to create your own monsters in any way you want, and the templates are only there to help you. For the sake of lore-consitency you may want to make the cases where "inherited" template is gained to be rare, but I'm pretty sure about some curses from a demon lord that made someone a natural lycantrope and other similar cases, to gaining "inherited" templete is not unprecedented, it should be a rare occurence that resulted from unique circumstances, not something that PCs may hope to recreate.
To become a Shadow Creature the G.M. can say that the N.P.C. wanted to merge with the essence of the Shadow Plane by using [4/5] Reincarnate or  Cyclic Reincarnation - the new body is made up of the surrounding materials, (in this case "Shadow stuff", ha, ha). All that it would take are reliable, (read : subjugated), subordinates to help with the "ritual" sacrifice and "shedding" of his old life/form in commitment to power over the shadows ... As this is a new body, it can gain new/replace many physical aspects, (different Race/bloodlines/heritage), so it is a body that inherited the Shadow Creature Template - there are no Mental Ability Score increases. Considering that Shadow Lords are stated to have originally been Humanoids, and that only Shadow Creatures can become Shadow Lords, there has to be a mechanism for Humanoids "inheriting" the Shadow Creature Template. If it is being born on the Shadow Plane, (having been infused by the Plane's essence), then the "rebirth" of reincarnation should suffice. The Shadow Lord Template is Acquired, so that is easy enough for a G.M. to apply, (and as it is not Inherited the Mental +4 Ability Score Bonus to Cha. creates no conflict).