If you save your current settings to a profile then you can always just load that profile back in.
I would save the current settings and then create a new REACT profile before letting REACT configure EAC.
REACT obviously sets the External compressor settings itself, but also sets a few other minor settings, as well as the file naming schemes. On the whole nothing major - it certainly won't mess with your drive setup or anything similar. The relevant code is below - you will be able to make as much sense of the keys as I can.
$p = "HKEY_CURRENT_USER\Software\AWSoftware\EAC\Compression Options"
RegWrite($p, "UseExternalEncoder", "REG_BINARY", "FF")
RegWrite($p, "ExternalEncoderType", "REG_BINARY", "14000000")
RegWrite($p, "ExternalEncoderProgram", "REG_SZ", @ScriptFullPath)
RegWrite($p, "ExternalEncoderOptions", "REG_SZ", 'REACT %o %s %d "%a" "%g" "%t" "%n" "%x" "%y" "%m" "%e" "%f" "%b" %r')
RegWrite($p, "ExternalEncoderExtension", "REG_SZ", "eac")
RegWrite($p, "ExternalEncoderCreateCRC", "REG_BINARY", "00")
RegWrite($p, "ExternalEncoderID3Tag", "REG_BINARY", "00")
RegWrite($p, "ExternalEncoderCheckReturnCode", "REG_BINARY", "00")
RegWrite($p, "ExternalEncoderDeleteSource", "REG_BINARY", "00")
$p = "HKEY_CURRENT_USER\Software\AWSoftware\EAC\Extraction Options"
RegWrite($p, "BackgroundExternalCompression", "REG_BINARY", "FF")
RegWrite($p, "NoCompressionWindow", "REG_BINARY", "00")
RegWrite($p, "BeepWhenDone", "REG_BINARY", "00")
RegWrite($p, "AutoSaveStatus", "REG_BINARY", "FF")
$v = RegRead($p, "FileNamingConvention")
If $v = "" Or $v = "%T" Then
RegWrite($p, "UseVariousFileNamingConvention", "REG_BINARY", "FF")
RegWrite($p, "OpenCDInfoDialog", "REG_BINARY", "FF")
RegWrite($p, "RetrieveCDDBOnUnknownCD", "REG_BINARY", "FF")
EndIf
RegWrite($p, "FileNamingConvention", "REG_SZ", "%D - %C - %N - %T")
RegWrite($p, "VariousFileNamingConvention", "REG_SZ", "%D - %C - %N - %T (%A)")