Buy a formation and change the unit to the type you want to have.
This can be done by:
- Buy a formation in 1940 (or whenever you want)
- Change the date to 'December 1949'
- Deploy units
- When you have the 1940-vehicle selected, click on 'Change the current unit to a different type' (Right panel, 10th row, middle)
- If necessary, change the nation - this is not necessary for your example
- All December 1949 units of the actual nation should be selectable.
Of course, this is the standard method for using those special 1949 units and it works 99% of the time.
Be careful. If the unit you replace has certain special codes attached to it such as elite, recon or secondline, those attributes wil be accepted by the replacement unit that you choose. Therefore, for example, if you replace a Scout Patrol with a Heavy Tank the Heavy Tank will have high infantry command values and recon status. This may be desirable in some cases but most of the time it is not.
Just be careful.
They struggled with a ferocity that was to be expected of brave men fighting with forlorn hope against an enemy who had the advantage of position......knowing that courage was the one thing that would save them.
Julius Caesar, 57 BC