I have some experience in intentionally magnetizing casing to increase the range of PMR. It is difficult to get equivalent monopoles greater than a few thousand microWebers. Larger poles will tend to self-demagnetize rather quickly. This is only marginally more than is sometimes left on the casing by magnetic inspection. Have you measured the residual magnetization of the casing you are currently using?
PMR requires an adequate signal to noise ratio to get a signature that can be interpreted. Typical MWD tools can only resolve 30-100 nanoTesla. Specialized wireline tools can resolve signals an order of magnitude less than that, which will also increase the detection range.
I have seen high magnetization on old wells in the North Sea, where apparently electromagnetic pipe handling equipment had been used.
We can speculate that the steel parts of a BHA could become magnetized by running through highly magnetizied casing. I doubt this will be nearly as effective as the intentional magnetization during magnetic particle inspection. This question can only be answered by actually measuring the residual magnetization of BHA components before and after each run.