I have not put snowflakes on my roof for several years (used AC snowflakes then) but the only thing I ever did was to zip tie the cords to my roof ridge vents to keep them from sliding down. Never had a problem with lateral movement. The other problem I had was water pooling in the internal parts of the snowflakes and then getting in the lights. With the Boscoyo flakes the wires on the back should allow water to run underneath the snowflake so that should not be an issue. SWMBO has stopped all my roof climbing or I'd still be doing it. sigh