Write bytecode to a method with ASM in java

I am trying to make something similar to Mixins (from the Minecraft mod loader Fabric) and what I made so far seems to work (doesn't throw any errors, I don't know how else to check), but I got stuck now that I need to write the bytecode back to the original method.

How do I do this?

My code;

/**
     * @param method1 The base method
     * @param method2 The code that should be added
     * @param descriptor The descriptor for both of the methods
     * @param access_level The access level for both of the methods (private, public, etc.)
     * @param pos The position to inject to
     * @param method1Class The base methods source class
     * @param method The base method as a Method object
     * @throws Exception when something went wrong
     */
    public static void mixin(MethodNode method1, MethodNode method2, String descriptor, int access_level, String pos, Class<?> method1Class, Method method) throws Exception {
        // Create a new method with merged characteristics
        MethodNode mergedMethod = new MethodNode(
                access_level,
                "mergedMethod",
                descriptor,
                null,
                null
        );

        // Merge the instructions from both methods into the merged method
        switch (pos){
            case "HEAD" -> {
                mergedMethod.instructions.add(method2.instructions);
                mergedMethod.instructions.add(method1.instructions);
            }
            case "TAIL" -> {
                mergedMethod.instructions.add(method1.instructions);
                mergedMethod.instructions.add(method2.instructions);
            }
            default -> {
                throw new IllegalArgumentException("Invalid mixin point provided!");
            }
        }

        // Recalculate the stack size and max locals
        mergedMethod.maxStack = Math.max(method1.maxStack, method2.maxStack);
        mergedMethod.maxLocals = Math.max(method1.maxLocals, method2.maxLocals);

        // Generate the bytecode for the merged method
        ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_MAXS);
        mergedMethod.accept(cw);

        byte[] bytecode = cw.toByteArray();

        method.setAccessible(true);
    }