I am sorry if this is already possible - I haven't added any backtest yet, but I'm going to.
The thing is that I am backtesting my EA's with 99% modelling quality (tick-by-tick data), as 90% is insufficient for scalping EA's. However, since there is a limitation of 2GB per file in MT4, I can only backtest 12-16 months at a time, so I would need to merge several backtests.
A hard thing about business is minding your own.