T SQL : Replace First or Last occurance of a string to a new one

DECLARE @Name VarChar(MAX)
DECLARE @StringToReplace VarChar(MAX)
DECLARE @NewString VarChar(MAX)
SET @StringToReplace = SPACE(1)
SET @NewString = ','

SET @Name = 'MARIJUN P. MASCARINASO'
SET @Name = 'MA. BEVELYN D DABILAU'
SET @Name = 'SHEERWINE JOEL QUARTIRU'

SELECT
    [Name] = @Name
    ,[First Instance of space] = STUFF(@Name, CHARINDEX(@StringToReplace, @Name), LEN(@StringToReplace), @NewString)
    ,[Last Instance of space] = STUFF(@Name, LEN(@Name) - CHARINDEX(@StringToReplace, REVERSE(@Name)) + 1, LEN(@StringToReplace), @NewString)