Harmonization of tensions.
In 4-part harmonization, the addition of a tension necessarily involves the elimination (or alteration) of a chord tone.
The goal in this case will be to enrich the chord without it losing the characteristics that define its harmonic function.
The notes that are easiest to replace are the root (which is assumed to be highlighted by the rhythm anyway) and the perfect fifth, which does not significantly affect the harmonic function (for example, the diminished fifth of a Ć chord is a decidedly important note).
The rule of thumb consists of eliminating the chord tone underlying the tension:
9, b9, #9 replace the root
13, b13 replace the (perfect) fifth
11 replaces the minor third (but there are some alternative solutions)
b5, #5 involve the alteration of the fifth.
The discussion regarding the #11 is a bit particular; this would actually involve the elimination of the major third, but the identity of the chord could suffer as a result.
One possibility is to eliminate the fifth or to play with the voicing of the chord (a parti late).
In any case, it remains a rather delicate case; it is no coincidence that in most arrangement books we find rare examples of harmonizing the #11 on a ā ...