begin{sagesilent}
    a = Integer(randint(1,5))
    end{sagesilent}
    setcounter{Seed}{sage{a}}

begin{sagesilent}
    import string
    with open('counters.tex', 'w') as f:
        s = string.Template(r'setcounter{Seed}{$seed}').substitute(seed=randint(1, 5))
        f.write(s)
        # more "s =" and "f.write()" as desired.
end{sagesilent}

InputIfFileExists{counters.tex}