It's not a good idea to hide such message.
If your block based on procedure then you can change locking procedure to avoid mark row as changed.
You can always play with SYSTEM.MESSAGE_LEVEL variable but this is also not recomended_.
I agree with kikolus rather than hide this message, you should find the cause and eliminate the cause. The "FRM-40654: Record has been updated. Re-query block to see change." error basically states that record displayed in your form is different from the record in the table. Some of the common causes of this error are:
1. Data truncation. Your data type and format of a column in Forms doesn't match the data type and format of the column in your table. Make sure your data type and precision of your item in Forms matches the database. For example, if you have a table column of type NUMBER(4,2) but your Form uses NUMBER(6) - you should add a Format Mask of 9999.99 to make them match.
2. If you have a trigger on your database table that updates a column value during insert or update - this could cause the table to be out of synch with the record displayed in your form.
These two examples are just a couple of the possible causes. If you have a My Oracle Support (MOS) account, take a look at Doc ID: 1003629.6 - Troubleshooting FRM-40654 for more causes and solutions to this error.