To operate on one entry of a matrix, select the entry, and choose the operation while holding down the CTRL key. That will perform the operation in place, leaving the rest of the matrix unchanged. Because you are in a word-processing environment, you can edit individual entries (just click in the input box and then edit) and apply other word-processing features to entries, such as copy and paste or click and drag.
Many of the operations on the Maple menu operate directly on the entries when applied to a matrix, as can be seen from the following examples.
Factor
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Evaluate
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Evaluate Numerically
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Combine + Trig Functions
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Evaluate
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