Definitely not illegal. Flex tubes behind the windows attach to the windows with clips : r/lego
LEGO MOC Ford Flex - Set of Five Colors by IBrickedItUp | Rebrickable - Build with LEGO
LBE 125 18.0-EC Nano Brick | OriginalFlex
Are there any other instances where pieces like flex tube or ribbed hose(pictured below) are cut in a Lego instruction manuel? : r/lego
BEHIND THE BRICK EPISODE:2 Lego Flex - YouTube
Lego Technic - Universal Set with Flex System 8074 - Használ
Sínek 60205 | City | Hivatalos LEGO® Áruházból HU
Lego Technic Compatible Parts | Lego Детали Technic | Parts Lego Technic Blocks - Model Building Kits - Aliexpress
adidas Originals Flex x LEGO® Shoes - Blue | adidas Deutschland
Technic, Flex Cable 7L : Part bb0008c07L | BrickLink
MOC Technical Parts 4pcs FLEX JOINT 6M, DIA24, MALE & FEMALE compatible with major brand for kids boys toy 44224 & 44225|Model Building Kits| - AliExpress
DUPLO 10825 - LEGO® DUPLO Miles Exo-Flex ruhája
Tutorial: How to make LEGO flex tube arms - YouTube
LEGO Sets with Part 75 Technic Flex-System Hose, Rigid 3mm D.