I think this is all just reinforcing where you got with Tom, but I wanted to clarify a couple of points.
1. For the Income entry, you can put the dollar amount on the Miscellaneous line, and assign any category. You are choosing "Other Inc" but you could choose "_IntInc" as well. That selection would not get overridden by the tax free status of the security. "_IntInc" is the normal category used for interest income in investment accounts. You are correct to avoid using the Interest income field which would become an "_IntIncTaxFree" categorization. The "_IntInc" entry would flow to a Schedule B tax line entry which may or may not be what you want. Your choice.
2. Return of capital "for the same amount". As a negative? A normal (positive RtrnCap) decreases the cost basis of the security. A negative RtrnCap increases the cost basis which is what you want to do, and what Tom is doing in his annual amortization. A negative RtrnCap must be entered through the Enter Transactions button, not as an inline entry in the transaction list.
Those two entries should cancel each other out in terms of cash. No step 4 should be necessary.
3. If you have increased the cost basis of the bond to par value by a negative RtrnCap, selling it at cost is the same as at par is that same as real life.