The aeenv file has no overall size limit in terms of bytes but it's contents are subject to certain limits.
There is a runtime limitation of 4095 load module lines and 8190 transaction code lines for the aeenv file i.e. these are the runtime limits for the Transaction Enabler (aefad) to be able to read the entire contents of a single aeenv file. If additional lines are required, then multiple aeenv files will need to be made available to the aefad. The number of transaction code lines is double the number of load module lines because a single load module may have both a transaction type of both flow and tran.
Currently the Gen Build Tool or Implementation Toolset (BT) will add an unlimited number of non-duplicate lines to the aeenv file i.e. the BT is not currently designed to check if the current number of lines in the aeenv will exceed the aefad runtime limits.
The BT will not add a new line to the aeenv file if it finds that the transaction type/code of the transaction being built is already in the file i.e. it will not add a duplicate. If an existing line with the same transaction type/code is found and the userid/password/database information is different to what is set for the transaction being built, then that line will be updated accordingly.