I open assembly dll, have found the place to change, changed, click Save Module and receive:
Instruction operand is null
Error calculating max stack value. If the method's obfuscated, set CilBody.KeepOldMaxStack or MetadataOptions.Flags (KeepOldMaxStack, global option) to ignore this error. Otherwise fix your generated CIL code so it conforms to the ECMA standard.
All files written to disk."
How can I save the assembly and the use it in app?
PS. In other words: I have found that I need to change up to 10 occurrences string "T" to "P".
I think probably I can do it with Hex Editor but with dnSpy it is easier.