For the first one try:
ActiveCell.FormulaR1C1 = "=CONCATENATE(TEXT(NOW(),""dd mmmm yyyy""),
"", "", CELL(""filename""))"

for the second use:
ActiveCell.Formula =
"=RIGHT(CELL(""filename"",A1),(LEN(CELL(""filename"",A1))-SEARCH(""]"",CELL(""fi\
lename"",A1))))"

It doesn't matter that you use 'FormulaR1C1' (rather than just
'Formula') in the first as you don't have any cell  references, but it
does matter in the second.