i activate developer mode and from it activate OEM Unlock and USB Debugging. then install twrp then \e\ costume rom. if that the bootloader unlocked, so yes. also rotted it in my way to try change logo image.
i change the permission manually from file properties i believe there's no other way. about param.bin file did you mean to see it. if that i will attached it to the post.
1- i try change the first splash image (samsung logo fixed image that apper at the start of booting), that's my target.Just to be sure we are speaking the same, what you are trying to modify is the first boot stage, not the boot animation, isn't?. The first splash images displayed in your model are part of the bootloader where param.bin is placed, you won't find them into boot, recovery, system nor another partition.
2- during my search inside phone rooted system folder i find by chance compressed file called animation take copy extract it (just to learn but i like \e\ os animation).
3- boot, recovery, system etc is from stock rom that i unpack it on pc. as you say before
"there's good chance something is wrong again with your file"
4- yoy say "The first splash images displayed in your model are part of the bootloader", there's any way to download stock bootloader? is it inside stock rom or it dowmloaded separately.
you know i keep replay to you and you keep try help me so i try search also and do not keep all work on you.