You can do it easily by selecting those keywords. Cut or Copy as per your requirment, Paste it into an exel sheet. Apply the CONCATENATE formula to the first keyword using square brackets.(any problem - go to exel help) Then just copy that formula to all cells. Copy those results and paste them again to your keyword box.
OR ELSE IF YOU WANT IT TO BE DONE IN GOOGLE ADWORDS ITSELF:
Log on to your Adwords account, Go to - Campaign Management > Tools > Find and Edit Keywords
1. FIND keyword(s) you'd like to change. - optional - Set filter(s) to narrow your search. The system will find keywords that match all of your filters. - You may leave any filter blank. To find all keywords in this account, simply skip this entire step. [this is the option where you will match/filter those keywords according to your requirment.]
2. CHANGE or view keywords that match these search filters. a)Change match type to: phrase match / broad match / exact match b)Remove keyword-level destination URL(s) c)Delete these keywords d)No changes right now. See results list.
* This option will delete the keywords with your old match type and create new keywords with your revised match type. Your new keywords will not retain the history of your old keywords. [using the a) option will convert the selected keywords to specified match type]
First-of-all copy all your keyword list in column A, with first keyword in A1 cell, type the formula =CONCATENATE("[",A1,"]") in the cell B1, and you will get desired result in column B. Now copy cell-B1 and paste it in the B column upto the last keyword of your list.