If I have a database field called ID and I have a number of cells in
that field, starting with GGL001, GGL002, and so on, and I have a
field called IDNew, what would my Cold Fusion code look like that
would take GGL001 and insert G001 in the IDNew cell (basically
removing the second G and the L) and then take GGL002 and insert G002
in the IDNew cell, and so on?

Which database are you using?

<!--------------------------------------------------------
This example will work with several database programs, such
as MS Access, SQL Server, Informix, Oracle.
--------------------------------------------------------->
<!--------------------------------------------------------
Declare an array...
--------------------------------------------------------->
<CFSET records = ArrayNew(1)>

<!--------------------------------------------------------
Get all records...

1) Replace 'myODBCDSN' in BOTH queries below with your 
   ODBC or OLE DB connection 
   to your database - under Cold Fusion Administrator -> ODBC 
   section. The connection to your database must have read and
   update permissions.

2) Replace 'myTableName' with the name of the table.

--------------------------------------------------------->
<CFQUERY Name="getMyRecords" DataSource="myODBCDSN">
	SELECT ID
	FROM myTableName
</CFQUERY>

<!--------------------------------------------------------
Set all records...
--------------------------------------------------------->
<CFLOOP QUERY="getAllCustomerIds">
	<CFSET records[ArrayLen(records)+1]=#ID#>
</CFLOOP>

<!--------------------------------------------------------
For each array element...
--------------------------------------------------------->
<CFLOOP Index="index" FROM="1" TO="#ArrayLen(records)#" STEP="1">
	<CFSET ID2 = records[index]>
	<CFSET IDNew = Mid(ID2, 1, 1) & Mid(ID2, 4, Len(ID2)-3)>
	<CFQUERY Name="updateMyRecords" DataSource="myODBCDSN">
		UPDATE myTableName
		SET IDNew = #IDNew#
	</CFQUERY>
</CFLOOP>

I think this is your answer, assuming you always want it to start with G:

<!--- JUST TO SET ID TO SHOW YOU --->
<cfscript>
sampleID = 'GGL001';
</cfscript>

<cfoutput>
'G#removechars(sampleID , 1, 3)#'
</cfoutput>