DX4WIN can be used to track QSOs when worked from different callsigns. To avoid merges, try to do the following:
If the QSOs were worked from different DXCC entities, use a separate .DXL file for each callsign (i.e. you operated from Alaska as KL7QRS then moved to the states where you operated as W0QRS).
If the QSOs were worked from the same DXCC entity, or you want to keep combined award statistics, use the same .DXL file for each callsign (i.e. your callsign changed from KA4QRS to WQ4ABC).
Group numbers can be used to separate callsigns within a log. You would assign a unique group number to each QSO made with a given callsign. For example, KA4QRS might be group #100 and WQ4ABC might be group #101.
Make sure that you are logging new QSOs with the correct group number! Go to File -> Preferences -> QSO and set the group number that matches the callsign you are using (Thanks David Kozinn, K2DBK).
Here is how Erkki Heikkinen, OH2BF created selections for award tracking. First, he started by assigning a unique group number to each callsign he has operated from:
Next, he created a new selection called "OH DXCC" and assigned some calls to it. He did this by finding the Group Number/Name and double-clicking on it. This assigned the group to the selection (indicated by the X to the left of the group name):
He repeated this for each group (call) he wanted to include in the selection:
When he was done, he clicked on "OK" to save this selection.
He did the same thing for the times he operated from France:
Now when he wants to view the QSOs in his log that he made only from Finland, he uses Filter -> Selection and selects his "OH DXCC" group, which will filter the log with only QSOs in the groups specified in the selection.
Here, Erkki, OH2BF, has no group selected (i.e. all QSOs). Look at his "Same Call" window when logging or searching for PY2NY - he can tell which call he used each time he worked PY2NY:
From Dick Flanagan K7VC:
If a group number is associated with the QSO being printed, the group name can be printed on this line, such as "1996 CW WPX contest". This option is selected by putting a double "percent" sign (%%) on one of the Label/Greeting lines in the label format. The location where this is placed determines where the group name will be inserted. Also, "Print Group Names" must be enabled at the time of printing in the DX4WIN intermediate print window. For more information on Group numbers, see GROUP NUMBERS - Filter example.