Ah, Eve, and here I bet you think Gene Simmons is the actress, not the fire-belching bass player.
Gary Moore (I “r” in Gary) is the former guitarist for Thin Lizzy who went on to his own solo blues guitar career. He is known for a firey heavy blues/rock style, and the fact that he owns and plays Peter Green’s 50’s Les Paul Standard Sunburst guitar - the Alpha and Omega of vintage guitars, worth a hundred thou at least - more because it was Green’s during his heyday with Fleetwood Mac (the FM before Buckingham and Nicks joined after Green went crazy - it’s a long story).
I would have to listen to Moore’s song before I comment specifically on what happened to change the tone, but the three most obvious options are:
He stepped on a boost pedal or changed to his over-ridden amp channel
He switched pickups - probably from neck to bridge, and might’ve had the volume higher on the pickup he switched to…
He switched guitars in the studio and spliced the tracks together in the final mix.
Any of these are very, very common and no big deal…
My vote is for number two. There is an increase in signal amplitude and the treble harmonic content is suddenly boosted without a major change in timbre. All of this is consistent with switching from the neck to bridge position pickup. It is also an extremely simple operation for a guitarist to perform in the middle of playing a song. There is also no change in acoustic ambiance (at T = 4:18) to indicate a live venue nor any swell of applause at the song’s end that would confirm this.
It happens right in the middle of a note. He switched pickups and the treble pickup has more gain. It could be a stomp box but doesn’t sound like it to me, and if it was a studio trick or a stomp box it would have happened at the beginning of the phrase. Instead, he does the triplet, hits the high note, then slaps the switch. Then he switches back at 5:36.
Sheesh, can you tell I’m waiting for my wife to get ready to go out? I need a hobby. Wait…this IS my hobby!