mmm, but the following statement from the manual drives me in different direction:

"The same asset can use up to 3 different brokers or price sources for trading, for live prices, and for historical prices. For this, up to 3 symbols can be entered, separated by exclamation marks '!'. They are accessible in the script under the names SymbolTrade, SymbolLive, SymbolHist. "

Are you sure?