don't try changing descr_names.txt and continuing saved game, its very unlikely to work.

if you just want name to appear as something else you could probably change
the text file
data/text/names.txt
so instead of
{Decius} Decius
make it
{Decius} Fred
make back up copy first

if you want to change names around more do it before starting new game.
you can remove names from descr_names.txt in that case but check that they aren't in the descr_strat.txt file or script if there is one.

if you want to add names to a faction add them in that file and also to the
data/text/names.txt file