No you can't do that, except if you keep the 1/10th of the signal provider's balance (a bit more actually, since you can only use up to 95% of it).
Or you can adjust the participation percentage in signal's settings, accordingly in order to keep a copying ratio of 10% always.
Copying trade, no.
You don't ever want constant lot size. You want constant risk and risk is a function of lot size, stop loss size, and value of the symbol.