I see that it is possible:

You have a powered ranger hero (for example, Bard with Black Arrow and 2 Dagger , and Unseen Strike ); you can play Hands Upon the Bow to kill Bolg before pass to 5a.

Is it not cheat?

All valid. No cheat.

Why would it be cheat? You are not targeting Bolg directly with player cards and thus circumvent his player card immunity.

Yes, not cheat then. But it seems that the finally of Bolg is to be until 5b step. If you kill before..., but great for me! lol

Only i wanted to corfirm if it was valid.

This could also be applied to kill The Nameless Fear in Flight from Moria. It would be difficult, but it should be possible with Hands Upon the Bow recycling (from Hama or the Book of Eldacar) and enough attack boosts. Someone posted a session report on BGG where Dunhere used Dunedain Marks, Support of the Eagles, Keeping Count, and Grave Cairn to kill the Nameless Fear. Nate French then ruled that Dunhere's targetting was a player card effect, and so The Nameless Fear was immune

For Flight from Moria, I think it's problematic to allow The Nameless Fear to be destroyed. Aside from broader story concerns, the mechanics of the quest tie into The Nameless Fear with A Foe Beyond , and Blocked by Shadow and Shadow of Fear are thematically connected to The Nameless Fear. One possible solution would be to use errata to add "Indestructible" to The Nameless Fear. Another would be to reverse the Hands Upon the Bow ruling, which hasn't yet become official in the FAQ.