Every time you click on "Start" in the Tester, MetaTrader reads the .ex4 file again. So you can keep MetaTrader 4 opened, replace the .ex4 file in background and it will always be fresh. That's why I made this Chrome plugin https://chrome.google.com/webstore/detail/fxdreema-download-files/lnlppnklledgeaafojedgemkdhjdgdkp
Of course, you should put those.ex4 files in the Data Folder directly - https://fxdreema.com/index/help/pics/terminal_data_folder.png
mq4 files are source code, they are not used by the Tester. But if you only have .mq4 file and you start MetaTrader, it searches for all .mq4 files that have no .ex4 file and generates their .ex4 files.... and that''s why MetaTrader is often slow to start.