Those "D1" displacements you mention are applied to the CNodes provided each SNB, not the SNB Node. The T1 in your Step 5 was included in the operating case (Step 1). In your example, the operating case shows a 2 mm displacement in X at, say, Node 200. Add the XSNB @ 200 with a CNode of 201. Define the X displacement of 2 mm for Node 201 (not 200). If you do this correctly, the load case of "operating"+D1 will show zero X load on the XSNB since both "ends" of the SNB are moving in unison. The load case of "operating"+D1+"occasional" will then show the occasional load,only, on the SNB.
[I do not think it necessary to define all 6 DOF as mentioned in Steps 2 & 4). Only the displacements along the SNB vector will be useful.]