When a special rule grants a Range boost specifically for targeting lands with specific traits/contents, like Shadows of the Dahan, does that apply to Range arrows within a Power's text?

When a special rule grants a Range boost specifically for targeting lands with specific traits/contents, like Shadows of the Dahan, does that apply to Range arrows within a Power's text?

No, that bonus is specifically for choosing the target of a land-targeting Power.
Use the Power as though the number in the "Range" box were increased or completely ignored (depending on the Range boost in question) and the extra target requirement were included in the "Target Land" box. In the case of Shadows of the Dahan, this means ignoring the Range number entirely (but not anything else in the "Range" box!) and adding "Dahan" to whatever else is already in the "Target Land" box.
This differs from general-purpose Range boosts, which apply to all Range arrows.
Though early printings of Sky Stretches to Shore use the word "targeting," the text of that Power has been revised to work like other Range-boosing Powers and is not subject to this restriction.