Does adding honey to bottled wine increase the alcohol content? I purchased a Montepulciano, added 80 grams of honey and some pepper, and then put it in the fridge. A glass of it after 24 hours seemed to me more alcoholic than what it was originally. 
Is it psychological, as I had read this was the case (but can't find the source right now, and I tend to think it's not true), or is the increase of ABV real?
Highly unlikely that the alcohol went up. Four reasons. 


The alcohol already in the wine is a barrier for the yeast to re-ferment.
The sulfites in the wine could inhibit refermentation if it hasn't dissipated yet. 
The cold temperatures that will also inhibit fermentation. 
Many commercial wines are sterile filtered so yeast counts are zero to very, very tiny. 


So, in 24 hours it's highly unlikely that it fermented again. Your perception of alcohol may be enhanced by the sugar that you added. High alcohol wines routinely taste "sweeter" to many people even though sugar levels are low. You might have tricked yourself into thinking sweet wine = higher alcohol.