Good Morning. Landsat images legacy, are designed for interoperable use between them. But the MSS and ETM + sensor are different in several respects. (Asusencia of the Blue band, spatial resolution, etc.) On some older items a Prosesa approval among these images are presented. Especially in later articles to the launching stage of Landsat 4
I agree with Dr Hein Van Gils on the fact that atmospheric corrections are not necessary all times. It depends on the objective of your study and on the methodology you follow.
If you only want to quantify the changes in a general way, you can classify each image separately (processing it as well as you could and quantifying the errors) then by knowing the area covered by each land use in each date you can quantify the changes between them.
In the case you want to compare both images pixel by pixel you should perform a geometric correction and may be a relative radiometric normalization will be necessary.