What is the difference between re-engineering and value engineering?

Re- Engineering is concerning the Design & Supervision.
Value Engineering is How to change or to modify in the Design Criteria and B.O.Q.
to reduce the budget without effecting the systems performance and have to respect the international codes with concerning the enviromental and hiegyen effects 

Re-engineering is a set of actions done for the design/engineering change.It is actualy done once the product engineering phase is over.It inclues,dreawing change,ECO and BOM change.Value Engineering is a technique used at the early stage of the product engineering.

A short and crisp answer would be; ‘Re-engineering’ is an inevitable process and the system must have to go through it however, ‘Value engineering’ is simply an option if you believe that adding new values would only improve the efficiency/performance of your system. Logically, there is a need to ensure that adding such values is not affecting the existing processes workflows of the system; a regression testing is recommended to avoid disappointments.

Value Engineering is a systematic and creative methodology that analyzes the function of items, services, or systems to ensure that the required functions are performed at the lowest possible overall cost.  (Overall cost includes the cost of buying, operating, and supporting the item, service, or system).