I don't really understand why you would want to change the column to numeric but retain a code of 0000 rather than 0. Presumably, 0000 means something other than 0, such as missing data, not applicable, etc. I would think that it would be better to create a new nominal variable indicating whether or not that code (and what it represents) is present, and then recode the original column so that 0000 becomes missing rather than 0. If I am not understanding what the data represents, then perhaps you don't really want it to be continuous data at all.