Cleaning List with data that is 45+days old

Hello, I'm hoping someone can help this newbie in the right direction.
I'm looking to clean some of my lists with data that is over 45 days old.
This is the process I did.
downloaded the entire list
cleared the list and confirmed.
removed all the records that were 45 days old from the downloaded list
Loaded the clean list back to the existing list.
The problem that I'm having is that all the status of the leads are now New.
Is there a way to load the leads back into the list while keeping their existing status?
I'm looking to clean some of my lists with data that is over 45 days old.
This is the process I did.
downloaded the entire list
cleared the list and confirmed.
removed all the records that were 45 days old from the downloaded list
Loaded the clean list back to the existing list.
The problem that I'm having is that all the status of the leads are now New.
Is there a way to load the leads back into the list while keeping their existing status?