F240 writing problem

I have a problem when I write F240.
My F240 board is a 4MHZ crystal oscillator, using DOS to writing with the default and the 10MHZ crystal oscillator setting.
Now I know that I need to modify the C240_CFG.I file. However, the minimum frequency of the file is PLL_MF_10. The contents of the file are as follows:

; Only ONE PLL Mult factor should be selected (set to 1). If more than one is
; selected only the last on the list will take effect. If none selected then
; default is PLL MF = 1.0

PLL_MF_10 .set 0 ; 1 : Select PLL Multiply value of 1.0
; ~
PLL_MF_15 .set 0 ; 1 : Select PLL Multiply value of 1.5
; ~
PLL_MF_20 .set 1 ; 1 : Select PLL Multiply value of 2.0
; ~
PLL_MF_25 .set 0 ; 1 : Select PLL Multiply value of 2.5
; ~
PLL_MF_30 .set 0 ; 1 : Select PLL Multiply value of 3.0
; ~
PLL_MF_40 .set 0 ; 1 : Select PLL Multiply value of 4.0
; ~
PLL_MF_45 .set 0 ; 1 : Select PLL Multiply value of 4.5
; ~
PLL_MF_50 .set 0 ; 1 : Select PLL Multiply value of 5.0
; ~
PLL_MF_90 .set 0 ; 1 : Select PLL Multiply value of 9.0
; ~

;NOTE: The Flash Programming algorithm assumes an internal cycle time of 50nS
; (i.e. 20MHz CPU clk) Value selected above should take this in account.

So, how do I configure it? Thank you so much!