Format mask - oracle forms- Forms [32 Bit] Version 11.1.1.4.0 (Production)

I have a multi item block and the dsp_values is 60 characters. (character field)

Now I am trying a put a new value that is number. I need to have a format mask. In oracle forms there is not set_item_instance_property for Format Mask.   I have 2 functions

select case when trim(TRANSLATE('99','0123456789', ' ')) is null
            then 'numeric'
            else 'alpha'
       end
from dual

SELECT CASE WHEN INSTR('-1.-2','-')>1 THEN 'alpha' --if minus is not the very first symbol then ‘alpha’
WHEN '-1.-2' LIKE '%.%.%' THEN 'alpha'--if more than 1 period then ‘alpha’
WHEN '-1.-2' LIKE '-%-%' THEN 'alpha'--if more than one minus then ‘alpha’
WHEN REGEXP_LIKE('-1.-2','^[-0-9.,]*$') THEN 'numeric' --if all symbols are digits, a period, or a minus then ‘numeric’
ELSE 'alpha'
END is_numeric
FROM dual

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How can I use this for the new value . No decimals allowed. Other values in that field are character. Enclosing the screen print. When I put the value 80.0 the other values change to #####
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