MarcEditor is able to edit or insert fixed-length data element fields like the 006 and 008 field. This is especially useful because MarcEdit creates templates for these fields based on the type of resource that the record describes. To access this utility, follow the steps below.

1. From the main menu, select MarcEditor. Then select Edit:
2. You can see that there are two options for these fixed length data fields: Insert/Edit 006 and Insert/Edit 008. Hover over the following and you will be given a list of options as below:

3. The options available are the same for each field, though the values will be different. I will walk through both editing and creating a 006 fields, though the basic procedures are the same for 008.

4. If you select edit, the following screen will appear:

5. Since the record used for demonstration is an electronic resource, the editor has already separated the elements of the fixed length field and sorted them. By clicking the blue links, you will be taken to the OCLC page describing the name of that particular element in the field.

6. If you would like to create a new 006/008 field, select the type of resource you are working with from the list in step 2. Once you have selected it, this screen will appear:

7. Again, the blue links will take you to the OCLC description of that value. Once you are finished editing, click OK. Whether it is a new record or an existing one, the fixed length field will be updated with your changes. 

This function is a variation of the Edit Subfield Data function, but geared towards editing fixed-data control fields. It involves a slight change in the user interface, which are explained in the following workflow. It is also relevant to note that because MarcEdit and the mnemonic format does not conform to a particular standard of flavor of MARC, it will allow you to enter anything into a control field regardless of whether it is compliant with MARC21 standards.

1. Open the .mrk file by selecting it in the folder, which should open the file in MarcEditor, or open MarcEditor from the MarcEdit home screen and select the file in File->Open.
2. Select Tools►Edit Subfield Data. While the dialog box is the same seen when editing and deleting subfield data, once you enter a control field like 008 or LDR into the Field box, the adjacent field will switch from subfield to position.
3. In the Position field, enter the position you would like to edit within the control field. Remember that entries in the control field are numbered starting with zero. If you would like to edit more than one position in the control field, type a colon followed by the number of positions you would like to edit. For example:

As entered, MarcEdit will edit the LDR field starting at the fifth position and continue for the three positions which follow it. It is important to note that the numbering of the control field starts with 0, not 1.

4. Enter the data you would like to replace within the control field. If you would like to add certain data regardless of what is present in the control field for each record, then there is no need to enter query data in the Field Data box.
5. Enter the text you would like to add to the control field at the positions specified in step 4. When you are finished, the dialog box should look something like this:

 As written, this operation will search for the string “cam” (in lower case) in LDR positions 5-7 and replace it with “zzz.”

6. Click “Replace Text.” Below are the results of the transformation:

These are two separate records with different information in the specified positions.

Below are the results of this operation. As you can see the LDR field with “cam” in the specified position was edited while the record with “nas” was not.

7. Should you want to undo this, click Edit > Special Undo.
8. To convert this edited record back into a MARC record from the Mnemonic format, select File > Compile File into MARC.  
9. You will be prompted to give the compiled record a name, as the creator of MarcEdit tends to favor the creation of duplicates rather than regularly modifying the same record.