public class BadClass {
    public String badCheck(String value) {
        System.out.println("123");
        return value;
    }
}

public class GoodClass {
    public static String goodCheck(String value) {
        System.out.println("321 " + value);
        return Objects.requireNonNullElse(value, "hello!");
    }
}

public class Application {
    public static void main(String[] args) throws Exception {
        ClassReader reader = new ClassReader(Application.class.getResourceAsStream("BadClass.class"));
        ClassWriter writer = new ClassWriter(reader, ClassWriter.COMPUTE_MAXS);
        reader.accept(new YourClassVisitor(writer), ClassReader.EXPAND_FRAMES);

        FileOutputStream out = new FileOutputStream(Application.class.getResource("BadClass.class").getFile());
        out.write(writer.toByteArray());
        out.close();

        new BadClass().badCheck(" test ");
    }

    public static class BadClassVisitor extends ClassVisitor {
        public YourClassVisitor(ClassVisitor cv) {
            super(Opcodes.ASM9, cv);
        }

        @Override
        public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions) {
            if (name.equals("badCheck")) {
                return new BadMethodVisitor(super.visitMethod(access, name, desc, signature, exceptions));
            }
            return super.visitMethod(access, name, desc, signature, exceptions);
        }

        private static class BadMethodVisitor extends MethodVisitor {
            public YourMethodVisitor(MethodVisitor mv) {
                super(Opcodes.ASM9, mv);
            }

            @Override
            public void visitCode() {
                mv.visitVarInsn(Opcodes.ALOAD, 1);
                mv.visitMethodInsn(Opcodes.INVOKESTATIC,"com/lampa/liqui/GoodClass","goodCheck","(Ljava/lang/String;)Ljava/lang/String;",false);
                mv.visitInsn(Opcodes.ARETURN);
            }
        }
    }
}