Granting permission on an altered table in Teradata

I have a table, which has two columns say A and B as part of the Primary index PI_AB. I have to alter the length of B column - increase it.

I was planning to alter the primary index to just have A, then drop the column B, re-create or alter it to desired length and then again make it the part of primary index.

I cannot drop the table because it has certain grants which I won't be able to give it gain. So, I wanted to know will altering the table like this, affect the grants given to other users? Is there any other way to do it, without affecting the grants present on the table?

Any help will be appreciated.