Can we set the local salary in a foreign currency?

Unfortunately no. The client and employee must agree what the salary should be in local currency and this becomes their fixed salary. However, the salary can be adjusted, but typically it can only be increased as lowering the salary requires agreement from the employee and may also raise red flags with tax and labor authorities. Nonetheless, the client can pay Establish Brazil in USD without any additional tax and even so Establish Brazil grant the employees payment in BRL currency.