Once older version (3.x) queries are migrated into latest version (7.0) queries, they can be restored (set back) to the 3.x version. The backup for any query created in 3.x will be taken when first opened for editing in 7.0 Query Designer.
This backup contains the last change done to the query using 3.x editor. Any changes done in 7.0 Query Designer will be lost on restore. When the query is originally created in 7.0, it can’t be restored to older versions as there is no 3.x backup available.

Queries can be restored to 3.x version using program COMPONENT_RESTORE.

For more information and the how-to-restore, please visit the SCN blog entry created by Mahesh Kumar and Brian Keenan. You can find their SCN entry here