Rmarkdown automatically use function on plots - r

Question

I'm producing an RMarkdown document where each chunk produces a plot.
For each of these plots, I'd like to apply a special formatting function that adjusts the way the title appears.
Is there a way to tell knitr/rmarkdown to apply this special function to each chunk's plot? For example, maybe there's a chunk option like {r, fig.function = adjust_title_position}?
The motivation is that I don't want to have to retype the function call separately for each plot (e.g. adjust_title_position(plot_42)) and, at the same time, I don't want to use something like lapply(my_plots, adjust_title_position) which would require all the plots to be defined in one place.
Below is a minimal example of the RMarkdown file to which this could be applied.
---
title: "RMD_Example"
output: html_document
---
```{r setup, include=FALSE}
# Load ggplot2
library(ggplot2)
# Define helper function
adjust_title_position <- function(p) {
# Shift the horizontal position of the plot title
p_built <- invisible(ggplot2::ggplot_build(p))
gt <- invisible(ggplot2::ggplot_gtable(p_built))
gt$layout[which(gt$layout$name == "title"), c("l", "r")] <- c(2, max(gt$layout$r))
# Prints the plot to the current graphical device
gridExtra::grid.arrange(gt, newpage = TRUE)
# Invisibly return the gtable object
invisible(gt)
}
```
```{r plot_1}
ggplot(mtcars) + geom_point(aes(x = wt, y = mpg)) +
labs(title = "Weights and miles-per-gallon")
```
```{r plot_2}
ggplot(iris, aes(x = Sepal.Length, y = Sepal.Width)) + geom_point() +
labs(title = "Sepal length and width")
```

Answer 1

You could reregister the print-method for ggplot-objects.
# Define helper function
adjusted_title_position <- function(p) {
# Shift the horizontal position of the plot title
p_built <- invisible(ggplot2::ggplot_build(p))
gt <- invisible(ggplot2::ggplot_gtable(p_built))
gt$layout[which(gt$layout$name == "title"), c("l", "r")] <- c(2, max(gt$layout$r))
# Prints the plot to the current graphical device
gridExtra::grid.arrange(gt, newpage = TRUE)
}
# Reregister print.ggplot
assignInNamespace("print.ggplot", adjusted_title_position, asNamespace("ggplot2"))