The SUBSTR() function requires CHARACTER string input. You cannot use it with a number without first converting the number into a string. If you don't make the conversion then SAS will and it will use the BEST12. format when making the conversion.
If you just want to DISPLAY the number with a fixed number of decimal places then use a FORMAT. Either attach the format to the new variable in the new dataset. Or use a FORMAT statement in the procedure that you are using that is going to display the number.
data want;
set have;
v1_want=v1_have;
format v1_want commax20.6;
run;
If you want to reduce the precision of the number then use something like ROUND().
v1_want=round(v1_have,0.000001);
If you want the missing value to display as - instead of . then you could change the MISSING option. But that would apply to ALL missing values, not just those in V1_WANT.
If you want you could create a custom format to display V1_WANT as '-' then missing and using COMMAX format otherwise.
proc format ;
value myfmt .='-' other=[commax20.6];
run;
Or you could make V1_WANT be a character string instead of a number.
data want;
set have;
length v1_want $20 ;
if v1_have=. then v1_want='-';
else v1_want=put(v1_have,commax20.6);
run;
