Instead of editing savegame with many saves to edit.... you can edit it in the main
Download first ESF Editor (Click Here)....After that open ESF Editor and click File>Open ESF
C:\Program Files\Steam\SteamApps\common\empire total war\data\campaigns\main and select startpos.esf
It depends of what directory you installed your Empire Total War....and always make a backup file copy paste the original to a new folder incase of error...
Click CAMPAIGN_CALENDAR... Just change 2 to 4 which means 4 turns per year....you can edit it in which you like 4,5,6,7,8 etc...and save it always make a backup file to avoid error
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In this picture i played Great Britain and i save it and it was 4 Turns and still 1700...
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