What I actually want is the dedicated calculation of the number of waypoints but you said that would be impossible so I was seeing if I could think outside the box a bit. Did I misunderstand what you meant?
It's not impossible, it's just very inconvenient within the current architecture and flow.
The number of waypoints is in the strictly read-only part of the data model (in the mod ruleset). Adding more read-only instances of a blaster launcher (as you suggested above) changes nothing, actually it adds even more complexity on top: the game would have to be additionally able to somehow temporarily replace underlying read-only rules of a battle item, which is basically like trying to kill a fly with a tactical nuke (not only an overkill, but also a complicated cleanup after the fact).
The calculation of the number of waypoints is a much cleaner approach, but there is no single point where this can be effectively done. The method, which returns this number is used on multiple places and not all of them can provide all parameters needed for calculation. Also, it is called multiple times even just during the actual usage in the battle and could return different results for different calls within the same "usage".
So, we would need to introduce a new modifiable attribute on a BattleItem (instead of RuleItem), and carefully go through the whole process and select where and when this number should be initialized, updated and used. This requires a relatively big refactor, which is possible, but not something Yankes or I are very interested in doing; unless a lot of people show interest.