Using legacy code in Unity 5.0

Due to an update with the android devices I am attempting to update some legacy code to display properly on the new hardware. The old code uses GUIStyle, and because of the type of android device it's only possibly to use more up to date versions of Unity.

The problem I currently have is that though monodevelop still agrees GUIStyle is valid, the Unity editor doesn't register it. However the legacy styles are still applied after build and run. I have tried modifying the style through the use of GUISkin both in code and in editor but the only effect it has had is to strip the GUI elements of their styling.

Due to time constraints and the size of the project an entire rewrite of the UI is not currently a feasible solution, is there anyway to restore the ability to modify GUI styles, whilst still being able to push and debug to modern android devices?