when the program is deployed, modifying the data structure

I really want to know what will happen if after deploying the program, I need to upgrade it and change some fields in the struct, such as the following situations.
The struct before my upgrade is like this.

#[account(zero_copy)]
pub struct ProtocolConfig {
    pub protocol_fee_rate: u32,
    pub whitelist_protocol_fee_rate: u32,
    pub whitelist_uuid: [[u8; 24]; WHITE_PUBKEY_SIZE_USIZE],
    pub future_use: [u8; 128], //for future use
}

I think there won’t be any issues if the upgraded struct becomes like this (using the for_feature_use field,), but I’m not completely sure.I want to know a definite answer

#[account(zero_copy)]
pub struct ProtocolConfig {
    pub protocol_fee_rate: u32,
    pub whitelist_protocol_fee_rate: u32,
    pub whitelist_uuid: [[u8; 24]; WHITE_PUBKEY_SIZE_USIZE],
    pub new_use:Pubkey, //new field
    pub future_use: [u8; 96], //sub 32 byte
}

Additionally,If i directly add a new byte to the current data structure without using the for_feature_use field, what will happen? Will the accounts created through PDA become invalid?like this

#[account(zero_copy)]
pub struct ProtocolConfig {
    pub protocol_fee_rate: u32,
    pub whitelist_protocol_fee_rate: u32,
    pub whitelist_uuid: [[u8; 24]; WHITE_PUBKEY_SIZE_USIZE],
    pub future_use: [u8; 128], //didnt sub 32 byte
    pub new_use:Pubkey, //just add a new filed(32byte)
}