Another option would be to replace "R" with something else first then add a replace of that with Revenue. Something like:
, {fn REPLACE(
{fn REPLACE(
{fn REPLACE(
{fn REPLACE(
{fn REPLACE(
{fn REPLACE(GEBH.gl_type,'A','Asset')}
,'R','#')}
,'#','Revenue')}
,'E','Expense')}
,'L','Liability')}
,'C','Capital')}
as 'Acct Type Desc'
You likely would need to do this for all the replacements.