If an airport operator has displaced a threshold,for what ever reason,shouldn't it be subject to notam,and subseqently any associated approach guidance system be notam'ed as U/S?.
In saying that,any visual approach is made at pilot discretion,usually in accordance with any AFM or company OOps manual.
I would be rather reluctent,apart from using local knowledge and experience,to use any approach guidance system that is associated with a displaced threshold.
In my neck of the woods,when a displaced threshold is in operation,it is marked with lights and ground markings,and in some cases,a portable TVASI or PAPI,which will be notamed with the actual glidepath the system provides.Again,refer to AFM and OOps manual for compliance(and relevant landing charts for that matter),otherwise,its a visual approach!