Alright, so I had my brother who's an IT professional come and have a look at this issue for me, and here is the solution he found after a couple of hours work. It took a bit of work to find where to place it, but rather than putting the following code
# User R Profile scrips
# My custom start-up code
myPaths <- .libPaths()
myPaths <- c(myPaths[2]) # switch nexus[1] to C[2]
myPaths <- c('C:/R/win-library/4.0', myPaths ) # add new path
.libPaths(myPaths) # reassigns the path
in to the source .rprofile code in the C:/Program Files/R/R-4.0.3/library/base/R file, he left that as it was and created a new .rprofile (text file) in the local "Documents" folder with the above code in it. Obviously this protects the integrity of the source code and also means that I'm going to have less (if any) issues when updating R/Rstudio.