protected void modifySingleInstructionContext(Address addr,
			RegisterValue contextValue, boolean mergeContext) {

		Register baseReg = contextValue.getRegister().getBaseRegister();
		if (!baseReg.isProcessorContext()) {
			throw new IllegalArgumentException("Invalid context register: " + baseReg.getName());
		}
		Listing listing = program.getListing();
		if (mergeContext) {
			ProgramContext programContext = program.getProgramContext();
			RegisterValue oldRegisterValue = programContext.getRegisterValue(baseReg, addr);
			if (oldRegisterValue != null) {
				contextValue = oldRegisterValue.combineValues(contextValue);
			}
		}
		listing.clearCodeUnits(addr, addr, true);
		getDisassembler().disassemble(addr, null, contextValue, true);
	}
Repair the context and re-disassemble the instruction at the specified address.
@param addr instruction address
@param contextValue new context value
@param mergeContext if true, the specified context value will be merged with the existing 
context at the specified address, otherwise the existing value will be replaced.
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/program/util/LanguagePostUpgradeInstructionHandler.java