To be fair, I see nothing in the RC that explicitly bans this although it definitely used to be a part of RC.
Uninherited timing points must be used to accurately beatmap the song's time signatures.
For this rule you might have to put some more timing sections down that have "Omit barline" checked in order to keep the time signature of the downbeats effectively intact.
Uninherited timing points must be the same in every difficulty of a beatmapset. Each point must have the same BPM and offset in each difficulty.
As a given you'd need to have that in every diff of the set.
There must not be extra uninherited timing points in any difficulty. These may accidentally affect main-menu pulsing, add unwanted sounds to the Nightcore mod, or cause timing to shift. Acceptable uses include:
Aligning beats of the Nightcore mod with the start of musical sections.
Accomodating for objects in musical sections requiring unsupported beat snap divisors (e.g. 1/5, 1/7).
It is not explicitly stated that increasing the amount of sliderticks is not an acceptable use although you might very well run into some barrier of "you can't do that" with about any Modder/BN/NAT as it used to be something that was more explicitly outlawed by RC.
Maybe read through the
timing related part of Ranking Criteria yourself and build your own opinion.
Personally I would instead try to enhance the slider with a storyboarded effect instead of adding more sliderticks as sliderticks hardly add significant gameplay value to a map and trying to push such a map to ranking would definitely give you a lot of trouble.