I would use a math macro (section 22.2 of Help > Math). Create the macro
somewhere near the front of the document (Insert > Math > Macro inside a math
inset). If the symbol you are bolding is always 'x', define a macro with an easy
to type name (say \XX or \bX) that has no arguments and inserts the LaTeX code
including the 'x'. If you have a few symbols, maybe do one such macro for each.
If you have a lot of symbols, create a macro (say \bv) that takes an argument
and then hit every vector over the head with it (replace 'x' with '\bv{x}'
etc.).
Paul
