Rather than trying to pad the text to make it not visible you should be using a translation table which has been around for many releases.
If I understand what you are looking for you want to set the value in the cell to some number 169xxx but have it display text.
You can do this by using the 'CellTblWidth and 'CellTbl$ properties which defines a translation table for the cell (width of each entry and values).
Here is a sample program that should help explain these properties:
0010 PRINT 'CS',
0020 LET x=10
0030 GRID x,@(10,10,40,10),FMT="[Prouct Planning]20 [Correct]12"
0040 LET x'autosequence=-1
0050 LET x'rowshigh=10
0060 LET x'colno=1,x'row=0 ! Change column 1
0070 LET x'celltype$="dropbox"
0080 LET x'text$="Harvest robot"+SEP+"Handpicked Select"+SEP+"Hytdroponics robot"+SEP
0090 LET x'celltblwidth=6
0100 LET x'celltbl$="169198"+"1682??"+"169???" ! The three values
0110 WHILE 1
0120 OBTAIN (0)'BI',*,'EI'
0130 IF CTL<>x THEN BREAK
0140 GRID READ x,col,row,value$
0150 PRINT "Changed col:",col," row:",row," to '",value$,"'"
0160 WEND