import re

variables = {
    '*FFullName*': 'Raz Smith',
    '*FFirstName*': 'Raz',
    '*FSurname*': 'Smith',
    '*Subject*': 'hello',
    '*Day*': '27',
}

text = '*Day* *Subject* to *FFirstName* *FSurname*'
var_input = re.sub(r'\*[^*]*\*', lambda x: variables.get(x.group(), x.group()), text)
print(var_input)
#expected outcome: input = '27 Hello to Raz Smith'