pour un oui ou pour un non
[По поводу и без.]
[По поводу и без.] is the short version of the full [По поводу и без повода.]
maybe it overlaps the meaning of "чуть что" only partially
[Чуть что] is [at the drop of a hat]
But when you use [at the drop of a hat] in your translation of [pour un oui ou pour un non] I feel, that you are wrong. I can not prove it, because I do not speak any French.
How are "в случае чего" and "чуть что" nuanced?
Unfortunatelly, noone told you the truth about real difference between
[чуть что] vs [в случае чего].
[в случае чего] means [in case of something]
[чуть что] means [in case of anything at the first slightlest sign of the case]
[чуть что] is the short version for the full [хотя бы чуть-чуть что-нибудь].
[чуть-чуть] = [the slightlest part] or ideomatically [a drop]
[в случае чего] does not mean, that you must react at the first sigh of danger. You can wait and try to solve the problem yourself or ask someone else.
Usually by [в случае чего] they mean backup tool for solving the problem, so called Plan B.
[Call me в случае чего] means [you can count on me, but I hope, that you can solve your problems yourself.]
[чуть что] does mean, that at any even slightlest sign or evidence of problem, you must contact the sayer of this words.
Usually by [чуть что] they mean the main tool for solving the problem, so called Plan A or the Main Plan or just Plan.
[Call me чуть что] means [you must call me as your first reaction for appearence of the problem, even if there is no problem and you just felt that something is not all right.]
Can we [чуть что] translate as [по поводу и без.]?
No, of course no.
Because [чуть что] must have [повод] = [reason] = [sigh of problem].
[По поводу и без повода] reaction is allowed in any case, if there is [повод] or even there is no [reason].
[По поводу и без.] has negative feeling as in French.
[чуть что] and [в случае чего] have nothing negative, but they have some feeling of problem solving, which can be considered as positive.