Hello there,
I don't know if the answer to this question is still relevant to you, but there are a couple of things that strike me as strange about your expression:
1) There seems to be an extra quotation mark in your first replace ""vges>=". Alternatively, if you wanted to keep the extra quotation mark, you would either need to escape it ("\"vges>=") or encapsulate the whole string in single quotes ('"vges>=')
2) The field placeholder for Python snippets is !FieldName! with no quotations around (or the value would be interpreted as a literal.)
Either of these could be giving an invalid syntax error. Given the above, I would write the expression as:
!Value!.replace('!', 'vges>=').replace('?', '.')
I hope this helps!