Hi
Yes you can define your Decimal field as below
[Decimal (2,1)] element Test_Decimal_01 : DecimalValue;
( check SDK document 1602 at page 192, 7.2.3.5 Decimal (Business Object Extension)
I am afraid that you can not change data type in maintenance mode.
Other work around you can do in absl
first convert decimal value into to string by using ToString() then use built-in string function to manipulate it as per your requirement.
Regards
Sunil