alouette:
That's a length of string question and I'm still not sure of your motives; why don't I attempt to answer the question that I think you are asking and we can continue from there.
The ability to perform any Category A procedure will be limited at some combination of density, payload, fuel etc. Depending on the procedure the limit will come sooner or later; the helipad procedure will limit earlier than the short field, will limit earlier than the clear area (runway).
Shawn referenced the case where it was safer putting a worker into a position with a helicopter than it was for him to climb up - this is sometimes called the 'Relative Safety Case'. However, it does depend upon the State of Operation whether that particular operation would be permitted with other than OEI OGE hover performance - it is likely in the UK that the higher performance standard would be required. Even though that particular operation is not within a Category A procedure it could be regarded as equivalent to PC1 as engine failure would have been accounted for.
Other Aerial Work tasks would not have the protection of such performance - the risk of engine failure is accepted in view of the fact that there is no exposure for passengers or third parties. Fire fighting comes into this category. There are no performance standard requirement for Aerial Work
I am not certain what you mean by HUMS but, for the purpose of this discussion let us assume that you mean engine monitoring such as that provided by Monitair or Altair (UMS). If all operations were to be in PC1, engine failure would have been accounted for and so there would be no need for engine monitoring. In the event that Commercial Air Transport (CAT) PC2 operations ‘with exposure’ were being contemplated, there might be a requirement depending upon the regulation - for example when operating in accordance with JAR-OPS 3.
If you genuinely do mean HUMS, it is likely that this would be a combination of UMS and vibration Health Monitoring (VHM) - which is only now coming over the horizon and is mainly being considered to address tail rotor failure issues.
In any event, it is unlikely that either of these pieces of equipment will add greatly to the weight of the Bo.
I am not a Bo105 expert and I’m sure that others can answer any specific question you have on Category A take-off masses - it is normal Flight Manual fare.