Replace file header containing escape characters - r

Question

I created a vignette for a package with following header:
---
title: "My package vignette"
output: rmarkdown::html_document
vignette: >
%\VignetteIndexEntry{MyPackage}
%\VignetteEngine{knitr::rmarkdown}
%\VignetteEncoding{UTF-8}
---
However, vignette format doesn't allow full functionalities allowed by html_document.
I would like to automatically change the YAML header in order to have the ability to knit the vignette in full html_document format (with options like toc_float: true)
I'm trying to read the .Rmd file with ReadLines and replace the header using gsub, but I'm struggling with escape characters / regex:
content <- readLines('vignettes/MyPackage.Rmd',encoding = 'UTF-8')
vignette_header <- "output: rmarkdown::html_document
vignette: >
%\\VignetteIndexEntry{MyPackage}
%\\VignetteEngine{knitr::rmarkdown}
%\\VignetteEncoding{UTF-8}"
normal_header <-
'output:
html_document:
toc_float: true'
gsub(vignette_header,normal_header,content )
Error in gsub(vignette_header, normal_header, content) :
regular expression 'output: rmarkdown::html_document
vignette: >
%\VignetteIndexEntry{ALPSYSparams}
%\VignetteEngine{knitr::rmarkdown}
%\VignetteEncoding{UTF-8}' incorrect, because of 'Invalid contents of {}'
Thanks for your suggestions, alternative methods to modify a file header with escape characters welcome.

Answer 1

Instead of modifying header, as a workaround I made two Rmarkdown files with different headers, and used child chunck option to insert the same Markdown body:
Vignette :
---
title: "My package vignette"
output: rmarkdown::html_document
vignette: >
%\VignetteIndexEntry{MyPackage}
%\VignetteEngine{knitr::rmarkdown}
%\VignetteEncoding{UTF-8}
---
```{r child=here::here('data/MyPackageVignetteBody.Rmd')}
```
Fully featured Markdown :
---
title: "My package fully featured Markdown"
output:
html_document:
toc: true
toc_float: true
---
```{r child=here::here('data/MyPackageVignetteBody.Rmd')}
```