If I close my short option position before the close, am I at risk of being assigned on that contract?

If you are holding a short position, there is no option on the TWS to "cover". Rather, you will simply place a buy order to buy back the number of shares or contracts you are short. For example, if you are short 100 shares, you can close your position by placing a buy order for 100 shares. You can also right click on your position at any time and use the "Close" button at the top of the right click window to initiate a closing order…

If the short call leg of a covered write position is assigned, the long stock position will be applied to satisfy the stock delivery obligation on the short call. The price at which that long stock position will be closed out is equal to the short call option strike price…

Traders using the tiered commission structure for futures may be subject to an overnight carrying fee, which is relative to the account's level of excess equity. Customers on the fixed structure for futures are not subject to this fee.

Overnight position charges are applied for each net futures contract, net short call futures options, or net short put futures options on a single underlying for each business day the net futures position is held overnight…

No. There is no provision for issuing conditional exercise instructions to the OCC. The OCC determines the assignment of options based upon a random process which is initiated only after the deadline for submitting all exercise instructions has ended. In order to avoid the delivery of a long or short underlying stock position when only the short leg of an option spread is in-the-money at expiration, the account holder would need to either close out that short position or consider exercising an at-the-money long option…