Hi, most Lexus alloys are the same spec bar some LS/CT models, so changing to another Lexus wheel is relatively safe.
Here's my wheel info for reference;
Lexus GS 450 h S190
2008, 2009, 2010, 2011, 2012
Wheel specs and tire sizes (2008 — 2012)
Bolt pattern (PCD): 5 × 114.3
Center Bore (CB): 60.1
Thread size (THD): 12 × 1.5
Diameter: 18 — 19
Width: 245 — 245
Aspect ratio: 35 — 40
Smallest — Largest tire size: 245/40R18 — 245/35R19
Rims sizes (2008 — 2012)
Diameter: 18 — 19
Width: 8 — 8.5
Offset: 41 — 45
Lifted from; https://sizewheeltire.com/lexus-gs-450-h-wheel-and-tire-sizes/
The one drawback with OEM wheels is that they tend to be tucked into the wheel arch rather than flush with the panel. A flusher fit will give you a more dished wheel if you don't increase the offset. There's a long wheel thread over on Club Lexus that you might find interesting.