Although I have no knowledge on how this “Aircraft evacuation slide” is constructed and how the subject UN 0403 Flares, aerial (5.3g X 2) is installed, PI 955 is applicable to UN 2990. On reviewing PI 955, only Div. 1.4C and Div. 1.4S are permitted to be installed. There is no mention about permitting installation of UN 0403 which is categorized as Div. 1.4G. Furthermore, even with Div. 1.4C and Div. 1.4S, the quantity is capped as not more than 3.2g per slide.
Consequently, you are unable to ship this slide declared as UN 2990 using PI 955. Notwithstanding how the slide is constructed, UN 0403 Flares, aerial must be removed from the slide and the slide is to be forwarded as UN 2990 by either passenger or cargo only aircraft, The removed UN 0403 is to be forwarded by CAO aircraft. UN 0403 is forbidden on PAX aircraft.