Ask your questions in this thread. I'll answer them here, and this post will be updated semi-regularly with the question text and answer to act as a 1-stop FAQ.
READ THE RULES TWICE-THROUGH LOOKING FOR AN ANSWER BEFORE ASKING A QUESTION PLEASE
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Since we are clan, if we use an inner sphere mech that would be available to a particular clan would the weapons be considered clan or inner sphere?
Use the tech base listed in the corresponding TRO for each unit. If you select a Royal Mongoose, for example, all equipment on the Mech is Inner Sphere-tech, unless customized as per normal campaign customization rules (free or WCP-based).
Is the Laser AMS Advanced or Experiemental?
Experimental, as per the chart on page 408 of Tactical Operations.
What version of the Targeting computer is being used; the version shown on Sarna.net or a different version?
Sarna.net is not a definitive rules source. Unless otherwise noted, use the rules found in Total Warfare (latest edition, plus errata) for all equipment rules, including the Targeting Computer.
How does replacing units work? Can I replace a medium Mech with a Heavy Tank or a Light ASF?
You must replace a unit with a like unit of the same type and mass category (Heavy Vehicle, Light ASF, Medium Battle/OmniMech, etc). You need not replace it with the exact same unit, but you must stay within the guidelines as per your initial force composition rolls. No combination of replacement and/or customization may take your total force BV2 over the 38,000-point cap.
EXAMPLE: Rob's Hellbringer H is totally destroyed. Which is unsurprising, considering it's a Hellbringer. Rob would like to replace the unit. He decides to replace the Hellbringer H with another Hellbringer H. This costs 115 WCP (50+mass of the unit).
Later, Rob's Hellbringer H is totally destroyed. Again. Which is unsurprising, considering it was also a Hellbringer. Rob would like to replace the unit. He decides to replace the Hellbringer H with a Summoner Prime. This costs 120 WCP (50+mass of the unit). He then double-checks that the total BV2 of his entire force is equal to or less than 38,000 BV. Note that he could only replace the Hellbringer with a Clan Heavy Mech available to his faction or on the General List. He could not have replaced that unit with a Stormcrow (medium Mech, not heavy), nor with a Mars tank (not a Mech unit). He COULD have chosen to replace it with a 75-ton Viper, however, as both of them are Heavy Mech units.
Finally, Rob decides to customize the Summoner Prime. He removes the LRM-15 and ammo (2 items) and replaces them with an equivalent weight of SRM racks (say, 3 racks) and a ton of ammo (1 item). He pays WCP for adding or removing a total of 6 items. He THEN checks to ensure that the new BV2 of the modified Summoner is still under the 38,000 BV cap. It is, so the Summoner Prime-M is added to his force list.
Do OmniMechs get a discount for switching from one canon configuration to another canon config (say, a Summoner Prime to a Summoner C)?
Yes. This is a change to the printed rules text and the Master Rules Thread will be modified accordingly. Total up the WCP cost for your new configuration as a normal OmniMech customization. Subtract 5 WCP from the total cost, representing your Techs increased efficiency at changing to a "textbook" configuration. This applies to switching between OmniMech canon configurations ONLY. Standard BattleMechs do not receive a discount for switching between canon Mech variants (a Marauder IIC to a Marauder IIC 2, for example).
Can we pay the WCP cost to change OmniMech configurations *ahead* of time?
No. Keeping track of which configurations you have "banked" is straying too far into the AccountTech it's been requested we avoid for this campaign. However, certain mission rewards may let you "bank" a "free configuration change" for your OmniMechs; those will be uncommon enough that it shouldn't rile too many feathers.