The goal of this is to be able to format only part of the text in a cell.

I am trying to create a line of text which changes formatting depending on a
number of variables. What I am after is a system which will turn a line of
text (e.g. llllllllllllll and be able to manupilate part of it by way of a
coded formula. (So if a value is entered the text gets formatted accordingly.
so if a value is entered for '4' in one cell the text is formatted to
something like LLLL(!in red)then continues as llllllllll.

Alternateively, I would accept an easy way of converting text into different
formats within the cell so I could say "If I enter in the number '4' then
make the first 4 letters in the text BOLD.

Can this be done?