This is an obscure use case, so I'm not surprised that there's nothing about this online. I already know how to type accent marks in general, and how to change keyboards. However, I was not able to find any way to type e.g. m̃ using the Lithuanian or ABC Extended keyboards. I thought option-N followed by M would work in ABC Extended, for instance, but it doesn't. Here is a complete list of the characters I would like to be able to type:
Note that only a subset of these pose an issue. For example, I can obviously type é, ȩ, and č in either of the keyboard layouts above.
Any advice is appreciated. I would prefer to not have to pick characters from the symbol selection table.