SDP Upgrading: does Upgrading have impacts to customize information or not?

SDP Upgrading: does Upgrading have impacts to customize information or not?

I have read the topic about upgrading from this link

it's talking about Upgrading need to upgrade from version to version and it doesn't talk about impact to customization. Does anyone please tell me about impact from Upgrading to customization fields?

Best regards,
Songtham.

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