A posteriori change of text size in ggpairs


My question is about setting the font size in the panels of the upper triangle of ggpairs which report correlations between continuous variables.
I know how to do that upon creation of the ggpairs object (ie, pm2 in the code below). However, I would like to be able to do that after the creation of the object (ie, pm1 in the code below). Any suggestion to modify the object after its creation?

#> Loading required package: GGally
pm1 <- ggpairs(iris, 1:3)

pm2 <- ggpairs(iris, 1:3, upper = list(continuous = wrap('cor', size = 2)) )