Database Splitting and Relinking excel linked tables

If you split the db, the links for linked Excel sheets will still work. Not sure which tables you're referring to re adding protection. If it's the Excel sheets, they haven't been able to be edited from within Access for many years (at least not easily).
If this

Kemidan2014 said:

if i add protection to the tables so they can not edit the tables themselves will the forms still be able to write data to the tables?

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refers to Access tables, then the usual approach is to not allow users access to tables nor anything else that would permit them to look at code or object design. Perhaps review Access security topic at this link Access Articles - Mendip Data Systems

Why don't you just copy the db, split it and test your Excel sheet connectivity and behaviours if you're not sure?
FYI, best practice is to link to sheets and put their data into normalized tables because of a)potential data type issues and b) the fact that spreadsheets are seldom good candidates for databases. Many Excel users fall into the trap of building db tables as if they were spreadsheets, which only leads to all sorts of problems. If you have not studied db normalization I suggest you do so.