Reversing and Shifting
Python 3.8 (pre-release), 65 bytes



lambda s,i,t:[s[(n:=[-t,t][i=='l']):]+s[:n],s[::(-1)**t]][i=='R']


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Abuses the de-facto ternary statement [a,b][condition].


If i=='R':


Return the string, read with step (-1)**t. This is -1 (reversed) for odd t and 1 (not reversed) for even t.

Else:


Let n be [-t,t][i=='l']. This is t when left-shifting and -t otherwise (right-shifting).
Return the string, spliced accordingly: s[n:] + s[:n]. Thanks to Python's negative indexing, this works like a charm for both cases.